Rotary molding apparatus and method

A method and apparatus for molding foamed materials for use as carpet underpadding is disclosed. In one aspect, the process and apparatus involves pulling a sheet of a foamed material through a first set of pull rolls at a first pull rate followed by heating the foamed material in order to decompose blowing agent present in the sheet thereby causing the sheet to expand or thicken. The heated sheet is then pulled through a second set of pull rolls which pull the heated sheet at a faster rate than the first pull rate in order to stretch the expanded sheet so that it returns to its original thickness. The surface of one of the rolls of the second set is provided with dimples or indentations uniformly spread on the surface thereof for producing protrusions on one side of the heated sheet. In one form of the apparatus, the roller with the dimples is cooled while the molded sheet is retained against this roller after formation of the dimples in order to provide cooling for the former to allow the protrusions to set properly. The molded sheet is further cooled as it is run along cooled rolls after which it is trimmed and collected.

FIELD OF THE INVENTION 
The present invention relates to the fabrication of molded underpads for 
carpets. 
BACKGROUND OF THE INVENTION 
Carpet underpads must generally exhibit the properties of cushionability, 
flexibility and durability in order to achieve their full utility. As 
such, carpet underpads usually comprise a foamed material having an open 
cell structure. Currently, carpet underpads are fabricated using foamable 
materials based on urethanes. A drawback to using foams based on urethanes 
is that when burned they give off noxious and poisonous gases such as 
isocyanate. In order to render the underpads safer, blowing agents (also 
referred to as foaming agents) based on butane have been used, but this is 
expensive and non-economical. Blowing agents based on fluorocarbons are 
also known but are not acceptable from an environmental point of view. 
SUMMARY OF THE INVENTION 
The subject invention provides a method and apparatus for producing 
externally molded carpet underpad from polyolefin based foams. The 
invention also provides an apparatus and method for producing internally 
molded cushionable products. 
In one aspect of the invention, a method of fabricating molded carpet 
underpadding includes providing a supply of closed cell foamed material, 
pulling the foamed material continuously from the supply using a first 
pulling means. The material is heated and pulled from the first pulling 
means by a second pulling means. The heated material is molded and then 
cooled. 
In another aspect of the invention, a rotary molding apparatus for molding 
closed cell foamed material includes a first pulling means for 
continuously pulling the material from a supply thereof at a first 
predetermined pulling rate. A second pulling means is provided for pulling 
the material at a second predetermined pulling rate. The apparatus is 
provided with a molding means for molding the foamed material. The molding 
apparatus includes a heating means located between the first and second 
pulling means for heating the material before it is molded, and includes a 
cooling means positioned after the molding means for cooling the material 
following molding.

DETAILED DESCRIPTION OF THE PREFERRED AND ALTERNATIVE EMBODIMENTS 
Referring to FIG. 1, an apparatus for producing molded carpet underpadding 
is shown generally at 10. The starting sheet material from which the 
molded underpad is produced is shown in rolled form at 12. The inventor 
has determined that closed cell materials such as foamed polyolefins, 
comprise excellent starting materials for carpet underpads. Specifically, 
those foamable polyolefin materials fabricated using an economical blowing 
agent which, upon decomposition of the latter (activation) does not 
produce toxic gases are the preferred starting materials. 
Canadian Patent No. 848,863 (Hosoda et al.) discloses various polyolefin 
based materials therein which may be used as starting materials in the 
subject invention. Some of the materials disclosed therein include low 
density polyethylene, high density polyethylene, polypropylene, and 
various copolymers such as ethylene-propylene, ethylene-vinyl acetate an 
ethylene-butane copolymer, to mention a few. 
In the initial fabrication of these foamed materials, not all the blowing 
agent is decomposed (utilized) with the result that undecomposed blowing 
agent is present in the final foamed sheet. The advantageous utilization 
of this residual blowing agent in one embodiment of the process and 
apparatus of the subject invention will be described presently. 
The rotary molding apparatus shown at 10 for fabricating molded carpet 
underpad includes a first set of opposed pull rolls at 14 and 16 for 
pulling sheet 18 from roll 12. A guide roll may be provided at 20 and a 
second pair of pull rolls 22 and 24 are provided wherein roll 24 includes 
the mold for molding sheet 18. Apparatus 10 includes a heater 30 located 
in close proximity to rolls 22 and 24 for heating sheet 18 prior to same 
being fed through nip 25 formed between rolls 22 and 24. Preferably, 
heater 30 is a radiant heater. 
FIG. 2 shows a section of molding roll 24 provided with a plurality of 
indentations or dimples 26 uniformly distributed over the surface of roll 
24 for molding protrusions on sheet 18. Extending from the surface of 
dimples 26 to the interior of roll 24 are channels 28 provided to act as 
vents for release of gas formed during the molding of the heated sheet. 
Channels 28 are in flow communication with channels 27 which provide air 
escapement when the material is compressed into the dimpled surface. It 
will be noted that molding roll 24 is hollow, but this is not shown in 
FIGS. 1 and 3 to 5 for the purposes of simplification. While the rotary 
apparatus disclosed above uses pressure to mold the foamed material, it 
will be understood that the molding could be accomplished solely by vacuum 
pulling, or by a combination of vacuum pulling and pressure. In such an 
arrangement, roll 24 would have a partial vacuum coupled to channels 27 
which, in conjunction with vent holes 28, provide the necessary suction to 
mold the material passing through nip 25. 
The temperature range to which the sheets must be heated will preferably be 
high enough to soften the material sufficiently in order that it may be 
molded and cause sufficient decomposition of the blowing agent and melting 
of the outer surface of sheet 18, but not so high that surface blistering 
or shrinkage of the foamed sheet occurs. A plurality of cooled rolls are 
provided at 32 while a trimming station is located at 34. The trimmed 
sheet may be collected in a variety of ways such as in roll form as shown 
at 38 in FIG. 1. 
As an optional feature, a thin polyethylene protective layer or film may be 
fused to the molded sheet. Referring again to FIG. 1, a thin laminate 
material comprising polyethylene sheet 50 is fed from a supply thereof 
around a guide roller and 52 and through nip 25 after being heated by a 
heater 51. This sheet is fed between sheet 18 and molding roll 24 so that 
it forms a film or layer on the molded side of sheet 18. As sheet 18 is 
pulled past heater 30, the outer surface of the side facing the heater is 
preferably heated high enough (in the vicinity of 300.degree. C.) so that 
it partially melts so that layer 50 is firmly fused or bonded thereto when 
layer 50 and sheet 18 pass through nip 25. This polyethylene layer 50 may 
be used to give the underpad greater strength, resilience and water 
resistance while inhibiting shrinkage and outgassing from the molded 
underpad. In another embodiment, both sides of sheet 18 may have laminated 
thereto the protective film. FIG. 3 illustrates an embodiment of the 
molding apparatus similar to that of FIG. 1 suitable for laminating a 
protective film or laminate to both sides of sheet 18 which includes a 
second heater at 70, a second supply of laminate material in the form of 
polyethylene film located at 72 and a guide roll at 74 for feeding film 
50'. 
FIG. 4 illustrates another embodiment of a rotary molding apparatus at 60 
of the subject invention which includes a series of rolls shown at 42, the 
purpose of which is to maintain molded sheet 36 against cooled molding 
roller 24 in order to provide better cooling and setting of protrusions 40 
(see FIG. 6). 
FIG. 5 illustrates a preferred embodiment of a rotary molding apparatus at 
80 which includes a series of water cooled rolls 82 in addition to an 
endless belt 84 wherein belt 84 may be substantially the same width as 
roller 24. A guide roll 86 is provided for guiding molded sheet 36 to 
trimming station 34. If belt 84 is not included, rolls 82 may be teflon 
coated in order to reduce friction between the molded sheet and the rolls. 
The rotary molding apparatus may also include means (not shown) for 
applying a protective laminate to one or both sides of the sheet, as in 
FIGS. 1 and 2. 
Referring again to FIG. 1, in operation, rolls 22 and 24 are 
counter-rotated each at an angular velocity sufficient to pull sheet 18 
therethrough at a higher rate than that at which rolls 14 and 16 pull 
sheet 18. Once sheet 18 passes by heater 30, the residual blowing agent 
contained therein decomposes causing sheet 18 to expand. Heater 30 heats 
the polyolefin sheet to a sufficiently high temperature in order to 
decompose the blowing agent as sheet 18 is being pulled through rolls 22 
and 24. The power output of heater 30 will depend to some extent on the 
color of the starting sheet. Specifically, a higher heater power output 
will be required for lighter colored sheets than for darker colored sheets 
since the former will absorb less heat than the latter. 
Sheet 18 may be pulled through nip 25 at a sufficiently higher rate than 
the rate of pull through rollers 14 and 16 so that heated sheet 18 is 
simultaneously molded and stretched so that it returns to its pre-heated 
thickness, thereby producing molded underpad 36 (see FIG. 6). As a 
non-limiting example, rolls 14 and 16 are rotated at the requisite speed 
necessary to give a pull rate of approximately 17 square feet/minute and 
rolls 22 and 24 are rotated at such speeds necessary to give a pull rate 
approximately 30% faster than that of rollers 14 and 16. In this way, the 
resulting molded underpad 36 will be approximately 30% longer than the 
starting sheet and roughly the same thickness. Thicknesses of the starting 
material for carpet underpad applications are in the range of 0.635 cm 
(1/4") to 1.270 cm (1/2") while widths are variable, depending on the 
preferred width of the rolls. 
One of the second set of rolls, preferably roll 24, may be cooled or 
maintained at a constant temperature lower than heated sheet 18 so that 
the resulting molded sheet is cooled after molding. Temperatures of 
20.degree.-25.degree. C. have been found suitable to give a good cooling 
effect but it will be appreciated that other temperatures in this 
vicinity, higher or lower, may also be acceptable. 
The molded underpad is then fed along the cooled rolls shown at 32 
whereupon it is fed into trimming station shown at 34 and trimmed to the 
desired width and collected into a roll at 38. 
It has been observed that by combining reheating of the polyolefin sheet in 
addition to calendering same results in an improvement in the back 
(unmolded) surface of the sheet making it generally smoother which renders 
the molded sheet easier to work with, when, for example, carpet is being 
laid over the latter. 
The operation of the preferred embodiment of the rotary molding apparatus 
of the present invention shown at 80 in FIG. 5 is similar to that of FIG. 
1 except that molded sheet 36' is maintained against roll 24 for 
approximately half the circumference of the latter. In this preferred 
embodiment, the material feed rate through apparatus 80 may be faster than 
the feed rate through apparatus 10 of FIG. 1. For example, feed rates of 
approximately 36 square feet/minute may be employed, with the higher rates 
possible due to the fact that molded sheet 36' is maintained against 
roller 24 for an extended distance thereby ensuring proper setting and 
cooling of the protrusions. 
The length and thickness of the molded material may be varied depending on 
the relative pull rates of the two sets of pull rolls. Thus, the length 
may be varied anywhere from 0-30% while the thickness can be varied in the 
range 0-10% higher than the thickness of the original starting material. 
The molded materials produced with the maximum length increase will be 
thinnest and vice versa. 
FIG. 6 shows a perspective view of a roll of molded sheet underpad 36 
provided with elongate protrusions 40. Since the purpose of protrusions 40 
is to increase the cushionability of underpad 36, the latter is normally 
laid on the floor with protrusions 40 against the floor surface. 
FIG. 7 illustrates an alternative protrusion pattern at 44 which may be 
molded into polyolefin sheet 36'. An advantage of this cross-shaped 
protrusion pattern is that the resulting molded sheet may be less prone to 
curling thus rendering the material easier to work with. 
In other embodiments of the process and apparatus for molding carpet 
underpad, both sides of the polyolefin sheet may be molded with the same 
or differently shaped protrusions. To achieve this, the molding apparatus 
of any of FIGS. 1, 3, 4 or 5 may be modified by substituting roll 22 with 
another molding roll (not shown) similar to roll 24 which is provided with 
the indentations necessary to give the desired protrusion pattern. 
It will be appreciated by those skilled in the art that the molding 
apparatus of FIGS. 1, 3, 4 or 5 may be used for molding carpet 
underpadding in a one step process wherein the sheet expansion step is 
excluded. Specifically, by heating the sheet material to a temperature 
lower than the blowing agent decomposition temperature, said material may 
still be molded by rotating rolls 14, 16 and 22, 24 at such speeds 
necessary to give the same pull rates. 
The starting material from which the underpad is molded has been 
illustrated as being a roll of foamed material. However, it will be 
apparent to those skilled in the art that other possibilities exist. For 
example, the starting material could be fabricated in sheet form using an 
extruder/heater assembly (not shown) placed adjacent pull rolls 14 and 16. 
The resulting extruded foamed sheet would be fed through pull rolls 14 and 
16 and molded in the manner discussed above wherein the blowing agent is 
decomposed by heating via heater 30. 
While the preferred embodiments employ rollers for pulling the material, 
other rotary pulling devices could be used such as endless conveyors, one 
of which could be run in opposition to a molding roller (not shown). 
It will be apparent that in addition to providing carpet underpadding, the 
molded polyethylene sheet of the present invention may be used for other 
applications. Specifically, being a good sound absorber, the sheet may be 
employed for sound proofing. Being waterproof, resistant to degradation 
and being resistant to mildew, the molded sheet may be used for coating of 
concrete and the like. It may also be used for heat insulation. The 
preferred thicknesses of the molded sheets would depend on the particular 
application for which the material is being produced. 
It will also be apparent to those skilled in the art that the thermal 
rotary molding apparatus disclosed herein may be applied to externally 
molding other materials besides the polyolefins. For example, any flexible 
moldable material should be moldable using the process disclosed herein. 
If such materials contain components which produce toxic products upon 
heating, the molding apparatus of the present invention may be readily 
provided with a suitable ventilation system 136. 
Similarly, while the present invention has been described and illustrated 
with respect to the preferred and alternative embodiments of the molding 
method and apparatus, it will be appreciated that numerous variations of 
the method and apparatus may be made without departing from the scope of 
the invention, which is defined in the appended claims.