Seamless, self-supporting waterbed liner unit and method of manufacture

Seamless, free-standing, self-supporting waterbed safety liner formed into a prepackaged unit. Sheets of liner plastic are laid-out, the corners folded into hospital corners, and strips of rigid riser material are placed to overlap the folded corners a few inches and secured thereto. The riser material is then rotated 270.degree. along their axes and bent along a medial score to bring the overlapped corner to the outside. Methods of folding the completed liner and installation are disclosed.

FIELD 
The invention relates to waterbed safety liners, and more particularly, a 
seamless, self-supporting waterbed liner and method of manufacture and 
folding for shipping. 
BACKGROUND 
Waterbeds today comprise a heavy vinyl mattress, usually of 20-gauge 
plastic, which is placed in a sturdy wood frame platform supporting a bed 
box comprising a continuous bottom of planks or plywood sheet and a 
substantial side rail perimeter frame. In the event the mattress is 
punctured, the water in the mattress could leak, damaging the bed frame, 
the floor, and other items wherever the water ran. Accordingly, a plastic 
safety liner sheet is usually disposed between the mattress and the frame 
sides and bottom before the mattress is installed and filled. This sheet 
is usually 8 mil vinyl plastic, and serves to contain any water which 
leaks from the mattress. 
There are variety of methods of manufacture and installation of waterbed 
safety liners in current usage. First, regarding manufacture, a principal 
method involves welding the corners of the liner to form a box corner. An 
appropriately sized sheet of plastic is folded diagonally to form a 
triangle, and an induction welding machine is used to form a weld line 
along the two folded corners parallel to the two sides (not the 
hypotenuse) of the triangle, and the small triangular scraps are cut off 
and discarded as waste. The sheet is then folded diagonally the other way 
and induction welded to form the other two corners. 
Second, as to installation, this corner-welded box liner is then shipped to 
the customer's installation site where a variety of installation methods 
are employed. Usually, the vertical sides of the safety liner are higher 
than the frame side. In one installation, the excess height is cut off, or 
folded over, below the side frame top edge, and taped in place. 
Alternately, the box liner may be stapled in place along its upper edge. 
Or, strips of wood may be nailed over the upper edge of the liner. Still 
another method involves cutting strips of cardboard from packing boxes, 
placing them adjacent the frame sides, tucking excess liner material over 
the top of the cardboard and between it and the frame sides, then securing 
it to the frame sides (by taping, tacking, or stapling through the liner 
and cardboard). In some instances such securing means are omitted, but 
keeping the liner in place while installing and filling the mattress is 
tricky. 
Recently, the "Tuckaliner" (U.S. Pat. No. 3,973,282) has become employed as 
an installation device and method. The "Tuckaliner" is a strip of 
resilient material, e.g., a plastic, having a first rolled longitudinal 
edge, a second longitudinal flat edge, and a bowed portion therebetween. 
The strips of the "Tuckaliner" are cut in the field to the bed length and 
width, and installed by nailing or stapling it midway up the frame sides 
with the rolled edge at the upper edge desired for the top of the safety 
liner. The welded box corner liner is then fitted into the bed frame, and 
the excess of the side risers are tucked in behind the rolled edge of the 
"Tuckaliner." The bow portion keeps the liner in place against the frame 
side by its spring action. 
All these taping, tacking, stapling or cut cardboard field installations 
are time consuming, labor intensive, and therefore expensive. Further, 
where stapling or tacking is used, the liner is punctured below its upper 
edge, permitting some leakage possibilities. 
A less field-labor intensive liner unit is the "Delta Star" type (made by 
Del Astra Industries, Stockton, CA). This is a welded, fitted liner that 
has rigid supporting strips self-contained in double side walls of plastic 
sheeting. The plastic sheeting completely surrounds the supporting strips, 
and the sheeting is then welded at the exterior bottom edge all around the 
periphery. Four or eight support strips are used, one or two along each 
side and the ends, and they are not joined at the corners. While this 
system is fast to install in the field, it is expensive to make as it 
requires more plastic sheeting, use of expensive welding equipment, and 
more factory labor. 
Another field installation method involves making a hospital corner in the 
liner plastic at each corner of the bed frame followed by taping or 
stapling it to the bed frame. The hospital corner is a method of field 
forming a relatively neat corner as compared to a manufactured, 
induction-welded box corner. This corner forming and securing is field 
labor intensive and expensive. Field labor is usually more expensive than 
factory labor. 
Accordingly, there is a need for a waterbed liner unit that can be easily 
made in the factory to precise dimensions, and which does not involve use 
of expensive induction welding equipment, yet which unit has 
free-standing, self-supporting side walls for easy and quick field 
installation, without the disadvantages of time and materials expense of 
employing securing means. 
THE INVENTION 
Objects 
It is among the objects of this invention to provide a seamless, 
free-standing, self-supporting waterbed liner unit that is simple and 
inexpensive to make, and which can be easily folded into a convenient 
shipping size. 
Another object is to provide a method of manufacture of a self-supporting 
waterbed liner unit which does not employ expensive plastic welding 
equipment. 
Still further and other objects of the invention will be evident from the 
detailed description which follows.

SUMMARY OF THE INVENTION 
A seamless, self-supporting, free-standing waterbed safety liner is formed 
into a prepackaged unit by laying out flat sheets of liner plastic, 
folding the corners into a pair of triangular areas with a Z-fold hospital 
corner therebetween. Then a rigid strip of riser material is glued to the 
base of the triangular areas. The riser is then rotated 270.degree. along 
its longitudinal axis to bring an overlap portion of the liner to the 
outside. The riser is scored (or two pieces are taped) to be bendable 
medially of its ends to form a right angle corner, with the tip of the 
hospital corner now lying on the outside of the riser and a few inches 
below the upper marginal edge of the riser. All four corners are done in 
the same manner to form the finished unit. This unit is then folded by 
bringing the gap between adjacent corner risers together along the center 
of the sides, and folding the pairs of corners together. The floor area of 
the liner is then wrapped tightly around the risers, and bagged for 
shipping. Field installation is "instant" in that the liner is simply 
taken from the bag, unrolled, unfolded, and the sides straightened. The 
liner is in position to receive the mattress bag. The liner unit is 
seamless, thus avoiding the need for expensive high-frequency induction 
welding machines. The liner unit is easy to install in the field as it is 
free-standing and self-supporting, resulting in negligible field set-up 
costs. The method of manufacture to form the corners and secure the riser 
thereto is simple, thus reducing labor costs. 
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
This description has reference to the accompanying figures which are 
illustrative and not limiting of the principles of the invention. 
FIG. 1 shows in perspective a completed free-standing, self-supporting 
waterbed liner unit 10 comprising a sheet of plastic 11 which has defined 
therein a floor area 12 and four self-standing risers 13, 14, 15 and 16 
around the perimetral edge 45 of the floor area 12. The risers comprise a 
rigid material, for example, 200-lb test corrugated cardboard, in the form 
of strips in which are folded medial their ends as at 17-20 to form the 
corners of the waterbed liner. The plastic sheet material 12 extends 
upwardly over the risers and is folded over the outside edge as shown at 
21. Each corner has a reverse hospital fold as at 22-25. By way of 
example, the rigid material forming the risers may be on the order of 7-9 
inches high. The liner may be glued to the upper outside edge of the rigid 
material forming the risers as best seen in FIG. 5c. 
FIGS. 2 and 3 show the corner details. FIG. 2 is an exterior perspective 
view showing the diagonal fold 25 adjacent the corner 20 of the liner as 
it is lapped over the top edge 63 of the rigid riser material 16. FIG. 3 
is a corresponding interior view showing the diagonal fold 23 forming a 
folded corner 18. It can be seen by comparing FIGS. 2 and 3 that any water 
which leaks out from a waterbed mattress contained in the space defined by 
the floor area 12 would not be able to leak outside as the corner is 
folded over, and the tip 26 of the corner is then trapped between the 
exterior of the waterbed liner and the inside of the waterbed frame (not 
shown). The corner fold can be reversed as seen at 25' and 23', that is, 
the fold tucked behind the plastic sheeting along the riser wall. We 
prefer to have end overlap 21' (FIG. 2) longer than side overlap 21 so 
that the tip 26' and lower edge of the corner fold 25 are secured by glue 
66 to the riser material. 
As can best be seen in FIG. 1, the risers may be formed from single sheets 
of rigid material, each of which is folded medial of its ends 27, 28 to 
form a corner such as corner 20. The gaps 29, 30, 31 and 32 permit folding 
of the entire unit as best seen in FIG. 6, and also provide for some 
adjustment for non-standard waterbed sizes. 
We prefer to glue the waterbed liner to the risers as part of the 
manufacturing operation, but the exterior lip forming the overlap 21 may 
be stapled or otherwise secured to the risers in any other suitable 
manner. We prefer, however, to not have the staples run through onto the 
interior of the liner to prevent loss of sealing integrity. 
Referring now to FIGS. 4 and 5, the invention also comprises a method of 
manufacture in which the corners are very simply formed, and which corners 
include the hospital folds as described above. The waterbed liner material 
may typically be a polyvinyl chloride plastic which comes in large rolls. 
The plastic is unrolled onto tables and cut off into a series of sheets of 
the appropriate size and formed into a stack 40 of sheets 11 (see FIG. 4). 
The sheets may be marked with corner identifying indicia, shown for 
simplicity in FIG. 4 as spots 41, 42, 43 and 44. These dots (which may be 
intersections of the lines as described below) represent the inside bottom 
corners of the waterbed liner. The lines 45, 45', 45", 45'" spaced 
inwardly from the edge margins of the sheet 11 define the floor area 12 of 
the waterbed liner. For example, this line may be spaced inwardly 
approximately 9-10 inches from the exterior margins of the sheet 11. Then, 
at each corner, a plurality of fold guidelines 46 is indicated. We prefer 
to stencil or print the fold lines onto the plastic sheet to assist in the 
folding of the corner. In the alternative, a sheet of guide material with 
the lines printed thereon may be slipped under the corner of the sheet so 
that the guidelines are visible through the plastic. 
Referring now to FIG. 5, in sequence from FIGS. 5a-f, a corner of the 
waterbed liner plastic is folded along first fold guideline 47 to form a 
triangular area 48. As can be seen in FIG. 5a, second fold line 49, third 
fold line 50, fourth fold line 51, and fifth fold line 52 are also 
identified thereon. The fold line 49 forms the corner fold line, that is, 
the vertical line which forms the inside corner, such as corner 18 as seen 
in FIG. 3. 
It will be noted that the third fold line 50 is drawn between the corner 
spot and the adjacent corner of the sheet of plastic 11. It will be noted 
that the fold lines 49 and 51 are diagonal lines as shown in FIG. 5a, are 
essentially the extensions of the perimeter lines 45, 45', respectively, 
and they lie intermediate the fold lines 47 and 52. The fold lines 50 and 
51 are chosen such that an appropriately sized hospital corner is made 
when the plastic is folded along those lines 50 and 52 (as best shown in 
FIG. 5b) so that fold line 51 is brought into alignment with fold line 49. 
As best seen in FIG. 5c, the resulting fold forms an isosceles triangle 
comprising areas 48 and 57 with the base line 61 extending diagonally 
across the original corner of the sheet 11. Glue 60 is applied, for 
example, with a brush or roller in a stripe approximately 1/2-2 inches 
wide adjacent the marginal edge 61. Thereafter, a rigid riser material, 
typically cardboard, is then laid down so that one longitudinal edge 
overlaps the edge 61 of the folded triangular area 48, 57 in contact with 
the strip of glue 60. This riser may be a single piece with a score 62 
medial thereof and is placed such that the medial score is aligned with 
the fold line 51. In the alternative, two strips of cardboard are taped 
together on only one side (on the side facing the viewer as seen in 5c), 
and aligned so that the transverse strip of tape joining the ends of the 
two strips 16a and 16b is in alignment with the fold line 51. 
Thereupon, as best seen in FIGS. 5d,e,f, the rigid riser board to which the 
waterbed liner plastic is glued is then turned over 270.degree. around its 
longitudinal axis and bent along the score or tape line 62 to form the 
corner 19 of the waterbed liner. This rotation and bending along the 
medial line 62 then forms the seamless, self-supporting safety liner for 
the waterbed. It will be noted that the glue line 60 is disposed on the 
surface of the overlapping portion 21 which contacts the outer surface of 
the riser 16 only as far as the intersection of lines 47 and 52 with the 
topmost edge 63 of the riser. Additional glue strips or areas, 64, 65 may 
be employed along the otherwise unglued areas if desired. This procedure 
is then repeated for the other three corners in a like manner. 
In the alternative, the reverse fold shown in phantom in FIGS. 2 and 3 is 
formed by folding line 50 over line 49 so that tip 26 lies between lines 
47 and 49. Further, a split difference fold may be made at the corners. In 
a split difference fold, there are basically two folds which extend partly 
along each of the two portions 16a and 16b of the riser from the corner 
19. This split difference fold is in essence a double hospital corner 
which may be folded in the same manner as described above. 
Turning now to FIG. 6, the completed waterbed liner as manufactured is 
illustrated in FIG. 6a. To fold the completed liner for shipping, the two 
sides are pushed inwardly toward each other as shown by the arrows at the 
gaps 30 and 32 between the riser sections. This is shown in FIG. 6b. The 
ends are then brought together as shown by the arrows in FIG. 6c trapping 
the midpoints 30 and 32 therebetween. The liner material hangs down in a 
truncated pyramid. The two corners 17 and 18 are then grasped and folded 
over to match the corners 20 and 19 as best seen in FIG. 6d. The resulting 
truncated triangular gathering 70 of the waterbed liner 12 is then wrapped 
around the stacked group of risers 17-20 as seen in FIG. 6e. The 
completely folded waterbed liner unit 75 is shown in FIG. 6f. This 
completely folded liner may then be put in a plastic bag for ease of 
shipping. 
In the field, the installer receives the folded and bagged seamless safely 
liner for the waterbed in the configuration of FIG. 6f. Reversing steps 
6e-a, the installer unrolls the floor portion of the liner as seen by the 
dashed arrows in FIGS. 6e-6b. This may be unrolled in the bottom of the 
actual waterbed frame, and the resulting instantly set-up liner which is 
free-standing, self-supporting and seamless is seen in FIG. 6a. The 
waterbed mattress may thereafter be placed on the floor area 12 of the 
liner and filled with water to complete the installation. As can be seen 
from the above description, we are able to eliminate the use of a 
high-frequency induction welding machine which is currently being used in 
the manufacture of the welded box corners and in the Delta Star type 
welded corner fitted liner that has supporting strips welded into the 
liner. We are also able to eliminate the field labor of cutting cardboard, 
tacking, stapling or taping the support, and tucking the liner behind the 
supports or behind the Tuckaliner type of liner retaining strips. 
In the alternative to gluing the liner to the riser material, the fold tip 
26 and the overlap strip 21 may be stapled to the outside of the riser, or 
taped thereto. In still another embodiment, the fold 24 and overlap 21 may 
be inserted in vertical slots cut in the upper 2 or 3 inches of the liner 
spaced along the topmost edge 63. 
It should be understood that various modifications within the scope of this 
invention can be made by one of ordinary skill in the art without 
departing from the spirit thereof. We, therefore, wish our invention to be 
defined by the scope of the claims as broadly as the prior art will permit 
and in view of this specification.