FABRIC LAMINATION TO CONCAVE SUBSTRATE Technical Field

This invention relates to a process of laminat¬ ing fabric to a concave, rigid substrate. In particular, it is directed to a method of lamination using a thermally activated adhesive that results in better bonding in the concave areas. Background Art

There are a variety of circumstances in which it is desired to laminate a fabric to a rigid, concave sub¬ strate. One example is automobile headliners. These are often formed of concave shells of fiberglass, corrugated paper compositions, or rigid foams, such as foams made of polystyrene, to which a fabric having a soft foam backing is laminated. See, for example, U.S. Patents No.

4,119,749 to Roth et al.. No. 4,077,821 to Doerfling, and No. 3,252,732 to Squier. A frequent problem with such articles is that delamination occurs in the concave areas. When the lamination is performed, the fabric is forced into the concavities by a male die or mold, creating some tension in the fabric. The fabric then pulls against the lamination adhesive after the die is removed. Often the foam will then separate from the substrate. This is called bridging. It can occur immediately upon release from the mold or it can occur days, weeks, or months later. It detracts significantly from the appearance of the product. To overcome the problem, it is common prac¬ tice to use high stretch fabrics, which exert less of a pull on the adhesive but which generally are more expen- sive than less elasticized fabrics. Even then delamina¬ tion sometimes occurs. Disclosure of Invention

The process of this invention laminates fabric to a substrate with little or no tension resulting in the fabric and, therefore, with a substantially reduced like¬ lihood of bridging occurring, even when a non-elasticized

fabric is used. The process comprises the following steps:

(a) coating the back of the fabric with a layer of heat activatable adhesive; (b) placing the fabric against the concave side of the substrate, with the adhesive next to the substrate;

(c) preheating a male die having a complemen¬ tary shape to that of the concave substrate, said die being perforated across substantially its entire contact surface;

(d) pressing the preheated die against the face of the fabric so as to push the fabric into the concave areas of the substrate;

(e) ejecting a shot of superheated vapor through the perforations in the male die at a pressure sufficient to drive the vapor through the fabric, thereby activating the adhesive and relaxing those areas of the fabric that are under tension;

(f) cooling the adhesive while maintaining the die pressure against the fabric, until the adhesive has set, thereby laminating the fabric to the substrate; and

(g) disengaging the die and the resultant laminated composition.

Even if not elasticized, the fabric is stretched in the areas where the male die pushes it into the con¬ cavities. But by use of the superheated vapor, preferably steam, the resulting tension in the fabric is then re¬ lieved, without shrinking the fabric back to its original shape. Thus the fabric takes on a new shape — that of the concavity — and does not pull against the adhesive bonds later. This process is especially useful in pro¬ viding complete and long-lasting lamination where a con¬ cavity is formed by the meeting of three planes, e.g. > as in each of the four corners of an automobile headliner, as well as in the headliner recesses for sun visors.

By preheating the male die and using superheated vapor to activate the adhesive, vapor condensation on the fabric can be avoided. This reduces or eliminates spot¬ ting of the decorative face of the fabric. Precisely how hot the die needs to be depends upon the activation tem¬ perature of the adhesive. Preferably, the die temperature will be high enough to warm the adhesive to near its activation temperature. For most adhesives it will be preferred that the surface temperature of the die be below the adhesive's activation temperature but within about 30 Fahrenheit degrees thereof, e.g., about 20 to 30 Fahrenheit degrees below the activation temperature of the adhesive. A die temperature of about 180 to 200° F. often is preferred. The preferred means of preheating the die is by use of electrical resistance heaters.

As stated above, the preferred superheated vapor to use is steam. Superheated steam is steam that exists at a temperature greater than the saturation temperature corresponding to its pressure. The temperature, pressure, flow rate, and duration of ejection of the steam into the fabric are to a certain extent interrelated. The pressure should be high enough to drive the vapor through the fabric. The combination of pressure, temperature, and time should be such that the adhesive will be activated across substantially the entire contact surface of the substrate and the tension in the fabric in the concave areas will be relaxed. Also, it is preferred that the conditions be such that the foam backing in these areas, if such is used, reach a high enough temperature that it will soften slightly, allowing it to conform to the shape of the substrate without tension. Usually the steam will have to have a temperature in the range of about 400 to 600° F. and a pressure of about 75 to 85 pounds per square inch gauge (psig) . (This is as measured before the steam contacts the die surface.)

The perforations in the die should be relatively small, e.g., having a diameter in the range of about 0.030 to 0.080 inch. There should be enough of the perfora¬ tions, and they should be spaced closely enough together, to ensure relatively uniform heating of the adhesive. The smaller the perforations, the closer together they should be. Generally, the perforations should be spaced not more than about 3/4 inch apart.

Suitable apparatus for practicing the process of the present invention are disclosed in International

Applications No. PCT/US 86/02807, filed December 30, 1986 ("Apparatus for Laminating and Shaping Foam ") and No. PCT/US 87/01111, filed May 18, 1987 ("Apparatus and Process for Shaping and Covering Cushion Foam"), which are incorporated herein by reference.

Fabrics that can be used in the process of the present invention include both knits and woven fabrics. The fabric needs to be gas-permeable, however, so as to allow the superheated vapor to pass through it. Circular jersey knits, raschel knits, and tricot warp knits can be used. Suitable woven fabrics include twills, flat woveπs, and velours. The fibers of which the fabrics are made may be polyester, nylon, rayon, wool, cotton, or elastomeric, i.e. "stretch", fibers—alone or in various blends. Preferably the fabric will be stretchable by a factor of at least about 5 percent, e.g., about 5 to 20 percent. This refers to the amount the fabric can be stretched at room temperature, without being permanently distorted.

The fabric may be backed or plain. Foam-backed fabrics often are preferred in such products. The foam normally is an open cell, thermoplastic, cushion foam, e.g., a polyurethane or polyolefin foam. Polyether-based polyurethanes and polyester-based polyurethanes can both be used. For automobile headliners the polyether-based polyurethanes hold up better, especially in hot climates, and are much preferred. Polyethylene is the most common

form of polyolefin foam used as fabric backing. Polyester-based polyurethane foams often have melting points in the range of about 300 to 325° F. Polyether- based polyurethanes melt higher, usually in the range of about 375 to 450° F. Polyolefin foams usually have melt points somewhere in the range of about 325 to 400° F. Preferably the foam will have a melting point higher than the activation temperature of the adhesive.

The only limitation on foam thickness is that it must be thin enough that the superheated vapor can pene¬ trate the foam adequately to activate the adhesive next to the substrate. Usually the foam will have a thickness of about one inch or less, often no more than about 3/16 inch. Foam-backed fabrics are well known in the art and can be manufactured by a number of different methods. Perhaps the most common method in use today is flame lami¬ nation. This entails passing a sheet of foam over an open flame to cause the sheet to become tacky on the bottom surface, and then pressing the tacky surface against the back of the fabric, using nip rollers.

The adhesive used to laminate the fabric to the substrate is a fabric adhesive which is activated at an elevated temperature, e.g., about 140°F. or above. Adhe- sives that are substantially solid at room temperature are preferred. It also is preferred that the adhesive be thermoplastic, i.e., can be remelted after once being set. The activation temperature of the adhesive should be low enough that the fabric will not be damaged. (Some fabrics can withstand temperatures as high as about 350° F., for short periods of time, without significant damage.) Dif¬ ferent adhesives may be preferred for different fabrics. Most often, however, the adhesive will have an activation temperature within the range of about 190 to 270° F. Use of a thermoplastic adhesive that melts in the range of

about 210 to 250° F. is most preferred. Thermoplastic polyamide adhesives are quite effective.

A normally solid adhesive can be applied to the fabric in particulate form, as a film, or as a web. Pre- ferably, it will be applied to the fabric in particulate form, i.e., it will be sprinkled on the fabric. This method of application permits greater uniformity of the adhesive coating than, for example, spray application of a liquid adhesive permits. The difference can be important in obtaining a smooth, even appearance in the final pro¬ duct. A commonly used prior art method of laminating a fabric to an automobile headliner shell involves the spraying of liquid adhesive on the rigid shell, following which the shell is sent through an oven to make the adhe- sive tacky. The shell then is placed in a female mold and fabric is laid over it. A male die is pressed against the fabric, but without the use of a superheated vapor. The die either is unheated or is heated by conductive heat. In addition to the bridging problem mentioned above, this often results in uneven application of the adhesive. If the adhesive layer is excessively thick in an area where there are imperfections, such as grooves or indentations, in the surface of the substrate, the imperfections will show through the fabric in the finished product. By using a powdered adhesive, e.g., having a particle size of about 100 to 400 microns, we are able to apply the coating with an accuracy of about + 0.1 gram/square foot, which makes for a smoother finish in the final product.

Another advantage in using a particulate adhe- sive is that it results in less waste. Spray application can result in a loss of as much as 30 percent of a liquid adhesive, due to spray falling beyond the edges of the substrate and to run-off. Spraying also releases more fumes than the sprinkling of powdered adhesive does. Some of these fumes can be unhealthy for humans or otherwise

dangerous. Relatively high melting adhesives that can be used in the present process sometimes could not be used in prior art laminations due to the risk of damage to the decorative facing fabric. Conductive heat having a tem- perature high enough to melt a normally solid adhesive underneath a foam-backed fabric often must be so hot it degrades the appearance or strength of the fabric. In the present process, however, small diameter jets of super¬ heated vapor, hot enough to melt the underlying adhesive, may pass through the fabric without damaging it. Indeed, if, in the present process, the temperature of the male die is kept below the melt point of the adhesive, then the surface termperature of the fabric generally will also remain lower than the adhesive melt point. The thicker the fabric, the greater the temperature drop from adhesive to fabric face. Lamination using conductive heat produces the opposite result. The face of the die normally has to be heated to above the adhesive's activation point, be¬ cause the fabric acts as an insulator. Thus the fabric is heated to at least as high a temperature as the adhesive, and usually higher. The present process permits the use of the more desirable hot melt adhesives, which often cannot be used in conductive heat lamination.

The substrate used can be any rigid material that will not melt or otherwise degrade when subjected to the action of the adhesive and vapor and the heat of the process. E.g., it can be made of metal, wood products, plastic, fiberglass, or rigid foam. It is preferred that the substrate be gas-permeable, so as to allow cooling air to be pulled through it after the fabric has been stretch¬ ed and the adhesive activated. The process is especially useful, for example, in laminating a foam-backed fabric to a contoured, compressed sheet of loose fibers bound to¬ gether, e.g., glass fibers or textile waste (also known as "shoddy"). The binder used is preferably a thermoset

resin, e.g., a phenolic resin, such a a phenol- formaldehyde condensation resin. Examples of such sheets, and methods of producing them, are disclosed in U.S. Patents No. 4,337,049 to Miller, No. 4,385,955 to Doerfling et al., and No. 4,466,848 to Ogawa, and in U.S. Patent Application No. 903,191, filed September 3, 1986, by George M. Elliott, entitled "Process of Forming a Con¬ toured Insulating Sheet."

In an alternative method of practicing the process of the present invention, rather than use a foam- backed fabric as a starting material, separate sheets of foam and fabric can be glued together simultaneously with the lamination of the foam to the concave substrate. In this three-ply lamination the fabric is placed over one side of the foam with a first layer of a thermally acti¬ vated adhesive in between the fabric and the foam; then the exposed side of the foam is coated with a second layer of a thermally activated adhesive. Generally the same requirements apply for the adhesive used between the fabric and foam as for that used between the foam and the rigid substrate. It is preferred, however, that a higher activation temperature adhesive be used between the fabric and the foam. Advantageously, the difference in activa¬ tion temperatures of the two adhesives will be in the range of about 20 to 50 Fahrenheit degrees. The fabric preferably will be somewhat elastic, e.g. , having a stretch value of at least about ten percent. The layered composite of fabric, adhesive, and foam is placed against the concave side of the substrate, with the second layer of adhesive next to the substrate. The remainder of the process is the same, with the die temperature preferably being within about 30 Fahrenheit degrees of the activation temperature of the adhesive between the fabric and the foam.

Brief Description of Drawings

For a fuller understanding of the process of the present invention, reference is made to the drawings that accompany this specification. Figures 1-7 schematically depict the preparation of a covered automobile headliner using the process of the present invention. Best Mode for Carrying Out The Invention

In Figure 1 a sheet of foam-backed fabric 10 is conveyed under a hopper 11, from which a powdered thermo- plastic adhesive 12 is uniformly sprinkled over the sur¬ face of the foam 13. The adhesive is applied at a rate of 18 grams per square meter. The adhesive is a polyamide having a melt point of approximately 220° F. Foam 13 is a sheet of open celled, polyether-based polyurethane, one- eighth inch thick. It is laminated to a decorative facing fabric 14, which is a woven blend of polyester and Lycra® spandex.

In Figure 2 foam-backed fabric 10 is conveyed past a radiant heater 15, which heats the powdered adhe- sive 12 just until it becomes tacky enough to stick to the foam 13.

In Figure 3 foam-backed fabric 10 is turned over so that the decorative facing fabric 14 is on the top.

In Figure 4 a rigid shell 16 for an automobile headliner is lowered into female die 17. The entire con¬ tact surface 18 of female die 17 is perforated with holes 19, which have a diameter of 0.040 inch and are spaced 1/2 inch apart. The enclosed cavity 20 behind female die sur¬ face 18 is connected to means (not shown) for pulling a vacuum. The concave shape of the contact surface 18 of female die 17 corresponds to that of headliner shell 16. Shell 16 is made of slightly compressed fiberglass, bound together with a thermoset phenol-formaldehyde resin. The porous shell measures about 60 inches wide by about 110 inches long and is approximately 9/16 inch thick, except at the edges 21, where it narrows to a thickness of about

1/8 inch. Poised above female mold 17 and headliner shell 16 is male die 22. The entire contact surface 23 of die 22 also is perforated, by holes 24, which are the same in size and spacing as holes 19 in female die 17. The con- tour of male die 22 is complementary to that of female die 17. Behind contact surface 23 of die 22 is an enclosed chamber 25, which is in communication with a source (not shown) of superheated steam having a temperature of about 450° F. and a pressure of about 80 psig. In Figure 5 adhesive-coated fabric 10 (from

Figure 3) is laid on top of headliner shell 16. The ex¬ posed layer of adhesive 12 is thereby sandwiched between foam backing 13 and headliner shell 16. Both die contact surfaces 18 and 23 are preheated by electrical resistance heaters (not shown) to a temperature of approximately 200° F.

In Figure 6 male die 22 is shown fully lowered into female die 17, thereby compressing foam-backed fabric 10 into tight engagement with concave headliner shell 16. When the dies are fully closed, the superheated steam is admitted to chamber 25, from whence it is ejected through the perforations 24 in male die 22. The steam ejection is continued for approximately 15 seconds. At about the 14th second a vacuum of approximately 1250 cubic feet per minute, at 7 inches of water, is pulled on female die 17 and is continued for about 6 seconds. As the vacuum is applied to female die 17, ambient air is pulled through foam-backed fabric 10 and headliner shell 16 through the gap around the peripheries of dies 17 and 22. The ejected steam heats the adhesive 12 to melting; the air purge helps cool and resolidify the adhesive. In only 20 seconds, lamination is complete; then, as shown in Figure 7, male die 22 is raised, permitting the removal of the finished headliner 26 from female die 17. (A comparable

prior art process would require a press time of approxi¬ mately 45 to 60 seconds.).

Figure 8 shows an enlarged view of the finished headliner 26, turned over from the position it occupied in female die 17. This is the orientation the headliner will have in an automobile, with the decorative facing fabric 14 on the underside.

Figure 10 is a life-size perspective view, in partial cross-section, of one of the four corners of the finished headliner shown in Figure 8. Resilient foam backing 13 adheres tightly and uniformly to porous fiber¬ glass shell 16, while decorative facing fabric 13 remains completely laminated to the foam. In contrast thereto. Figure 9 depicts a corner of a prior art headliner formed of the same materials, but using conductive heat and a liquid adhesive, rather than superheated steam and pow¬ dered adhesive. As can be seen, after removal of the headliner from the mold, the adhesive 12a has given way and foam 13a is loose in the corner of shell 16a. It is contemplated that the process depicted in

Figures 1-8 can be performed in a semi-continuous manner using a roll (not shown) of foam-backed fabric 10, which would remain uncut until the pressing step (Figure 6). Each side edge of the fabric might be held by a row of upstanding pins carried by a conveyor belt (not shown). In this manner the fabric can be held taut while it is pressed into the female die, so as to lessen the chance of wrinkling.

In making automobile headliners and the like, the process of the present invention allows the fabric to conform more closely to the contour of the substrate, even when the substrate has relatively deep concavities. This frees the manufacturer to use a broader array of designs than can be implemented with prior art processes.