U.S. patent number 3,907,193 [Application Number 05/458,838] was granted by the patent office on 1975-09-23 for plastic folding containers and process and apparatus for making same.
This patent grant is currently assigned to Autoplex Corporation. Invention is credited to Joel Heller.
United States Patent |
3,907,193 |
Heller |
September 23, 1975 |
Plastic folding containers and process and apparatus for making
same
Abstract
Flexible fold lines in semi-rigid and rigid plastic sheet
material (e.g., polyvinyl chloride) are provided with stress-relief
indentations so that the tensile and compressive strains normally
produced at the folds are substantially relieved, thereby
permitting efficient production of a variety of sheet plastic
articles such as folding containers and the like. The stress-relief
indentations are simultaneously formed on opposite surfaces of the
sheet material at the fold line by an apparatus having a die
containing a heated scoring blade and a platen which can be
preheated by contact with the heated scoring blade prior to
insertion of the plastic sheet material between the scoring blade
and platen. The temperature of the scoring blade and platen and the
pressure with which they are brought to bear on the plastic sheet
material disposed between them during the scoring operation are
such that the thickness of the sheet material is substantially
reduced at the fold line by compression and removal of material
without any substantial lateral displacement flow thereof away from
the fold line. In this way, parallel indentations are formed on
both surfaces of the sheet material at the fold line which serve to
relieve the tensile strains on the outer fold surface and
compression strains on the inner fold surface normally produced
when the material is bent about the fold line.
Inventors: |
Heller; Joel (Greenlawn,
NY) |
Assignee: |
Autoplex Corporation (Roslyn
Heights, NY)
|
Family
ID: |
23822276 |
Appl.
No.: |
05/458,838 |
Filed: |
April 8, 1974 |
Current U.S.
Class: |
428/156;
229/930 |
Current CPC
Class: |
B31F
1/08 (20130101); B65D 5/4266 (20130101); B29C
53/063 (20130101); B65D 2301/20 (20130101); B31B
50/252 (20170801); B29C 37/0057 (20130101); Y10S
229/93 (20130101); Y10T 428/24479 (20150115); B29K
2069/00 (20130101); B29K 2067/00 (20130101); B29K
2027/06 (20130101) |
Current International
Class: |
B29C
53/00 (20060101); B31B 1/25 (20060101); B31B
1/00 (20060101); B29C 53/06 (20060101); B65D
5/42 (20060101); B29C 37/00 (20060101); B65D
005/00 (); B65D 043/16 () |
Field of
Search: |
;220/31S,62,16A,16B
;229/30,38,2.5,DIG.4 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Moorhead; Davis T.
Attorney, Agent or Firm: Pennie & Edmonds
Claims
I claim:
1. A container comprising walls of plastic sheet material joined to
each other by fold lines comprising heat-scored linear indentations
on opposite faces of the sheet material, the thickness of the sheet
material between the indentations being substantially less than the
thickness of the sheet material away from the fold lines, the
density of the sheet material between the indentations being
substantially greater than the density of the sheet material away
from the fold lines, and the quantity of plastic material along
each of said fold lines being less than the quantity of material
through an equal cross-sectional area of sheet material located
away from the fold lines, said fold lines being further
characterized by the absence of ridges of laterally displaced
plastic material along the heat-scored linear indentations.
2. A container according to claim 1 wherein:
the plastic sheet material is thermoplastic sheet material; and
the thickness of the sheet material between the heat-scored linear
indentations is between about 25 and about 75 percent of the
thickness of the sheet material away from the fold lines.
3. A container according to claim 2 wherein:
the thermoplastic sheet material is selected from the group
consisting of poly(vinyl chloride), polycarbonate and polyester;
and
the thickness of the sheet material between the indentations is
between about 40 and about 60 percent of the thickness of the sheet
material away from the fold lines.
Description
BACKGROUND OF THE INVENTION
This invention relates to the art of forming fold lines in
semi-rigid and rigid plastic sheet material, and more particularly
to a process and apparatus for forming fold lines in plastic sheet
material to facilitate the formation of novel products such as
plastic boxes or containers.
With the development of a variety of synthetic plastic materials
available in sheet form, attempts have been made to utilize them in
the fabrication of folding cartons or boxes. Thus, for example, as
reported in Modern Packaging, April, 1964, page 161 and October,
1966, pages 127-129 and Paper, Film and Foil Converter, October,
1966, pages 68-71, attempts were made to make a "see through"
folding box of transparent synthetic resin sheet material such as
poly(vinyl chloride) by cutting out a blank, folding it along
scored fold lines, cementing together two opposite free edges of
the blank, and then flattening the assembly so that the item can be
transported and stored. When ready for use, the flattened box is
erected, filled with material, and then closed by inserting folding
flaps formed on the bottom and top ends of the box blank.
Previous efforts at forming fold lines in a sheet plastic carton
blank to provide the necessary flexibility at the fold line to
permit setting up the box from the flat blank have proved to be
unsatisfactory due to the fact that damage or undesired
discoloration (e.g., blushing or whiteness) of the sheet material
occurs at or near the fold line during folding. Also, when the box
blank is flattened for storage or shipment or when the flattened
box is erected preparatory to filling, the panels and flaps of the
box do not remain in the desired condition but rather, tend to
revert to a state intermediate of the flattened and opened
conditions due to the springiness or elastic recovery tendency of
the material being used to form the box. This elastic behavior
tends to interfere with the automatic folding, filling, and closing
operations currently being practiced in commercial packaging
facilities using paperboard boxes and cartons.
Scoring of sheet material to form a fold line has heretofore been
performed by bringing a scoring blade against the sheet material,
which is backed up by a platen so that the sheet material is
deformed out of the plane of the sheet to form the desired score
line. In forming conventional paperboard boxes or cartons, the
blades are unheated, and the fold line is formed by what is
referred to as "cold scoring," as described for example in U.S.
Pat. Nos. 3,137,217 and 3,529,516. Similar cold scoring techniques
have been attempted in connection with plastic sheeting as
indicated, for example, in U.S. Pat. Nos. 3,334,802; 3,292,513;
3,594,464; and 3,350,492. Unfortunately, cold scoring has
heretofore proven unsatisfactory when used in conjunction with
thermoplastic sheet materials due to the fact that the cold
deformation of these sheet materials along the intended fold line
appears to produce a strain hardening of the material, resulting in
fracturing and crazing along the score line, when the sheet
material is folded or set-up into the carton. This problem is
recognized in U.S. Pat. No. 3,589,022, which describes attempts to
obviate this difficulty by employing heated scoring blades to form
the desired score line indentation on one side of the sheet. It
has, however, been found that even where the scoring blade is
heated and brought down on one side of the sheet material
sandwiched between the scoring blade and an unheated platen, with
the scoring blade penetrating the sheet material on one side of the
sheet, there is still produced a weakness and crazing discoloration
of the plastic material, though perhaps not as great as in
connection with cold scoring.
Other methods of hot-scoring plastic sheet material are described
in U.S. Pat. No. 3,379,814. The use of plastic molding techniques
for imparting fold lines is described in U.S. Pat. Nos. 3,132,649
and 3,201,145.
Therefore, a need has existed in the packaging field for a method
and apparatus for imparting fold lines to plastic sheet material to
permit the production of folding containers and boxes which are
free of the aforesaid drawbacks heretofore experienced in the prior
art.
Accordingly, it is an object of the present invention to provide an
improved fold line for use in plastic articles, with the material
being subjected to minimum distortion at the fold line when the
material is folded, thereby improving its strength and
appearance.
Another object of the present invention to provide an improved
process for forming fold lines in plastic sheet material which
impart sufficient flexibility to permit setting up a carton or box
from a flattened or knocked-down condition prior to filling without
causing damage, tensile or compressive stresses, strain hardening,
crazing, or discoloration of the sheet material at or near the fold
line while at the same time permitting the box to remain flattened
until opened and thereafter remain in the intended open condition
with minimum elastic recovery to facilitate machine loading.
Another object is to provide an improved plastic folding container
from sheet material whose walls are joined at fold lines which
impart sufficient flexibility to permit setting up the container
from a flattened or knocked-down condition prior to filling without
causing damage, tensile or compressive stresses, strain hardening,
crazing or discoloration of the sheet material at or near the fold
lines while at the same time permitting the box to remain flattened
until opened and thereafter remain in the intended open condition
with minimum elastic recovery to facilitate machine loading.
Yet another object of the invention is to provide an apparatus for
cutting plastic sheet container blanks and imparting fold lines
thereto having sufficient flexibility to permit setting up the
container from a flattened or knocked-down condition prior to
filling without causing damage, tensile or compressive stresses,
strain hardening, crazing, or discoloration of the sheet material
at or near the fold line while at the same time permitting the box
to remain flattened until opened and thereafter remain in the
intended open condition with mimimum elastic recovery to facilitate
machine loading.
These and other objects of the invention as well as a fuller
understanding of the advantages thereof can be had by reference to
the following detailed description, drawings and claims.
BRIEF DESCRIPTION OF THE DRAWINGS
The specific details of the method, product and apparatus of the
invention will be particularly described in conjunction with the
accompanying drawings wherein:
FIG. 1 is a perspective view of a section of a sheet of plastic
material with strain relief indentations formed in accordance with
the teachings of this invention;
FIG. 2 is a cross-sectional end-view of the sheet of material shown
in FIG. 1 bent through 90.degree., illustrating the nature of the
strain relief provided by the invention;
FIG. 3 is a cross-sectional end-view of the sheet of material in
FIG. 1 bent through 180.degree., illustrating the nature of the
strain relief provided by the invention;
FIG. 4 depicts a photomicrograph taken through a cross-section of
plastic material having strain relief indentations formed in
accordance with the teachings of this invention;
FIG. 5 is a top plan view showing a typical box blank formed in
accordance with the teachings of the invention;
FIG. 6 is a top plan view of a platen provided with heat-retaining
strips along the desired fold lines, with the platen shown arranged
for simultaneously forming two box blanks of the type shown in FIG.
5;
FIG. 7 is a plan view of the die used in connection with the platen
of FIG. 6 with the single line thicknesses in the drawing
representing the edges of the cutting blades of the die, and the
double line thicknesses representing the edges of the scoring
blades of the die; and
FIG. 8 is a cross-sectional view through the die and platen of
FIGS. 6 and 7.
SUMMARY OF THE INVENTION
The foregoing objects are achieved according to the present
invention wherein a fold line in plastic sheet material is provided
with strain relief indentations at opposite sides of the sheet
material at the fold line to relieve both tensile and compressive
stresses normally produced at opposed surfaces of a fold line
during bending, thereby minimizing crazing, material weakening, and
stress discoloration or whitening during folding. The sheet
material thus treated can be formed into a box or carton blank
which can be shipped in a flat or knocked-down condition for set-up
or erection when desired for use without exhibiting the undesirable
elastic tendency to assume a position intermediate of the fully
opened and closed conditions.
The fold lines are provided with stress relief indentations by heat
scoring applied at opposite faces along the intended fold line.
Heat scoring of the plastic sheet material is accomplished
according to the present invention by the use of a heated scoring
blade and a platen member. The platen surface supporting the
plastic material, against which the scoring blade is brought to
bear in a transverse direction, is also heated in the vicinity of
the score line. The scoring blade is brought against the previously
unheated material to be scored at a pressure and temperature which
substantially reduces the material thickness between the scoring
blade and the platen, desirably to a value of between about 25 and
75 percent of the original thickness, and preferably to a value of
between about 40 and 60 percent of said original thickness. In this
way, fold lines in plastic sheet material can be readily formed
without requiring the use of expensive equipment, and are of a
strength and cost which permit the fabrication of plastic boxes and
cartons of significantly improved appearance and which are
competitive with previously employed paperboard containers.
The temperature of the scoring blade and platen and the pressure
with which they are brought to bear (preferably with minimum dwell
time) against the plastic sheet material must be adjusted,
depending upon the composition of the plastic material, so that the
stress relief indentations are created through compaction and
removal of material from the site of scoring without any
substantial lateral displacement flow thereof away from the fold
line. Although suitable temperature and pressure combinations can
vary over a wide range, it is desirable to maintain the temperature
of the scoring blade within .+-. 10.degree.F. of the deflection
range of the sheet material and to adjust the pressure accordingly.
The meaning of the term "deflection range" used herein is that
employed by the American Society for Testing Materials in its
Standard D648-72. Deflection ranges for a variety of plastic sheet
materials suitable for use according to the present invention can
be found in the Modern Plastics Encyclopedia, pages 549-569 (1971-2
edition). Although the precise chemical or molecular behavior of
the plastic sheet material at the scoring temperatures found
satisfactory for practicing the invention is not clearly
understood, it has been empirically determined that at temperatures
more than about 10.degree.F. above the maximum deflection range
temperature for a given material set forth in the ASTM deflection
ranges, or more than 10.degree.F. below the minimum ASTM deflection
range temperature, satisfactory scoring is more difficult to
attain. Thus, when the temperature exceeds by more than
10.degree.F. the upper limit of the ASTM deflection range
temperature, a tackiness results tending to cause adhesion between
the scoring blades and the material. At temperatures more than
10.degree.F. below the lower limit of the ASTM deflection range,
crazing of the material tends to occur with apparent strain
hardening, producing brittleness.
The present invention can be practiced in scoring a wide variety of
plastic sheet materials suitable for use in making boxes and
cartons, including but not limited to thermoplastic sheet materials
such as those containing polystyrene, polyethylene, polypropylene,
nylon, formaldehyde polymers, poly(vinyl chloride), poly(vinylidene
chloride) and related vinyl polymers, nitro cellulose, ethyl
cellulose, cellulose acetate, cellulose acetatebutyrate,
poly(methyl methacrylate), polyesters, vinyl acetate, and
acrylonitrile-butadiene-styrene resins. Such materials can be
composed of homopolymers, copolymers or various blends thereof;
they may also contain various additives known in the art, including
colorants, plasticizers, heat stabilizers, extenders, fillers, and
inhibitors against degradation due to oxidation, ultraviolet light,
and the like.
Among the commercially available PVC sheet materials, Stauffer's
X-15 rigid PVC film, Tenneco's Mirrex PVC clear film and American
Hoechst Corporation Genotherm 1001/1002 PVC films have been found
to be eminently suitable for use in the present invention. Plastic
sheeting consisting of a copolymer of vinyl acetate and vinyl
chloride together with vinylidine chloride is also suitable for use
in the present invention.
Satisfactory results can be obtained utilizing a variety of plastic
materials, of which the above are given by way of example, ranging
in thickness from less than about 0.005 and greater than about
0.015 inch. The apparatus of the present invention is designed so
that the scored material is substantially reduced in thickness
between the scoring blade and platen. Desirably, the material is
reduced in thickness to between about 25 percent and about 75
percent of the original thickness of the material, so that the
depth of each indentation on opposite faces of the material along
the score line is between about 12.5 and 37.5 percent of the total
thickness of the material away from the score line. Preferably, the
scored material is reduced to a thickness of between about 40 and
60 percent of the original thickness of the material, so that the
depth of each indentation on opposite faces of the material along
the score line will be between 20 and 30 percent of the thickness
of the material away from the score line. The width of the
stress-relief indentations generally depends upon the thickness of
the plastic sheet material being scored; the thicker the material
the wider the scoring blades. In particular, a scoring blade width
of between about 0.025 and about 0.030 inch produces satisfactory
stress-relief indentations on sheet material between about 0.005
and about 0.010 inch in thickness; a scoring blade width of between
about 0.040 and about 0.045 inch works well on sheet material
between about 0.010 and about 0.015 inch in thickness. As noted,
earlier, the temperature of the scoring blades is desirably (but
not necessarily) maintained within about .+-. 10.degree.F. of the
deflection range of the plastic sheet material being scored.
Ideally, the temperature of the platen member along the intended
score line is the same as that of the corresponding scoring blade,
although the platen in actual practice can be as much as about
50.degree.F. cooler than the blade. In order to reduce the cost of
operation, it is preferred to maintain the scoring blades at a
temperature near the lower end of the deflection range. In order to
obtain desired scoring blade temperatures, it is advantageous to
maintain the heaters on the presses at a temperature approximately
100.degree.F. higher than the desired scoring blade temperature, as
indicated later in the examples.
It is a feature of the present invention that the heat which must
be applied at the platen side of the material can be obtained, if
desired, by securing heat-retaining metal tapes to the platen along
the desired fold lines, aligned with the scoring blades, using a
suitable adhesive. The thickness of these tapes is not critical and
tapes having a thickness of about 0.015 inch are found to be
suitable. By bringing a heated scoring blade against the tape
before positioning each sheet of material to be scored on the
platen, the tape can be sufficiently heated so that continuous
production is obtained by relying on the heat previously stored in
the heat-retaining tapes.
Photomicrographic examination of the score lines under polarized
light indicates that there is an increase in density at the score
line. Without wishing to be bound by theory, it is believed that
when the material at both sides of the score line is heated and
compressed at a temperature and pressure according to the present
invention, the crazing conventionally encountered in cold scoring
and in heretofore known hot-scoring is eliminated, and a laminar
continuity of molecular arrangements is attained within the plastic
material. Examination under polarized light further indicates that,
when the material is bent about the score lines formed in
accordance with the invention, since the radius of curvature at the
outer surface of the bend is substantially reduced by the
indentation at this outer surface, the tensile strains at the outer
surface of the material are substantially reduced. Similarly, the
indentation on the inner surface at the bend reduces compressive
strains thereat due to the fact that there is no material to be
compressed at the inner material surface. Furthermore, it is
observed that the strain relief indentations formed by heat scoring
under pressure at the fold line according to the present invention
are brought about by a combination of compaction of plastic
material between the indentations (resulting in increased density
thereat) and physical removal of material from the scoring site.
Surprisingly, these phenomena are unaccompanied by lateral
displacement flow of material to the sides of the score line, which
would result in the formation of a pair ridges at the fold line as
is observed, for example, in the process taught by U.S. Pat. No.
3,379,814. Such ridges are undesirable since they detract from the
appearance of the material at the outer surface of the fold and
tend to interfere with the operation of the stress-relief
indentation at the inner surface of the fold.
As mentioned earlier, it has been discovered that provision of
stress relief indentations on opposite surfaces of a rigid or
semi-rigid plastic sheet material along the intended line of fold
serves to facilitate the production in the sheet material of a fold
line which, when the material is folded, minimizes undesired
cracking or crazing and discoloration of the material. This
apparently results from the fact that the radius of the curvature
of the outer surface of the material is substantially reduced at
the indentation, thus mimimizing the tensile stress at this outer
surface, and reducing the strain in the material. Similarly, at the
interior corner of the fold, the absence of material at the
indentation eliminates any material which would otherwise offer
resistance to compressive forces of the surface material adjacent
this inner fold, thus minimizing compressive stresses and strains
in the material.
DESCRIPTION OF THE DRAWINGS
Referring now to the drawings, like numerals will be employed to
designate like parts.
As shown in FIG. 1, a sheet of thermoplastic material 10 is
provided with strain relief indentations 12 and 14 on opposite
surfaces of the sheet material along a desired fold line.
As seen in FIG. 2, the strain relief indentations 12 and 14 serve
to eliminate material at the points of maximum stress when the
sheet material 10 is folded about the score line. Thus, on the
upper surface viewed in FIG. 2, the radius of curvature of the fold
is reduced, and any tensile strain which would normally tend to be
greatest at the outer corner of the fold is accommodated by the
surface along indentation 12. Similarly, the compressive strain
normally produced at the inner corner of the fold is reduced, since
material is removed at indentation 14, thus eliminating material
which would otherwise be subject to compression and preventing the
transmission of any compressive forces between the inner surfaces
11 and 13 on the sheet material as viewed in FIG. 2.
Referring to FIG. 3, the strain relief indentations 12 and 14
continue to eliminate material which would otherwise be present at
the points of maximum stress when the sheet material 10 is folded
180.degree. about the score line. The tensile strain which would
normally build up at the outer corner of the fold is accommodated
by the surface along indentation 12. In a like manner, the
compressive strain normally created at the inner corner where sides
11 and 13 join together is accommodated by stress relief
indentation 14.
Referring now to FIG. 4, there is depicted a photomicrograph, in
transverse cross-section, of a thermoplastic sheet material, such
as poly(vinyl chloride), which has been heat-scored using the
process and apparatus of the present invention. As can be seen from
FIG. 4, stress relief indentation 12 appears circular in
cross-section to reflect the corresponding curvature (preferably
semi-circular) of the working end of the scoring blade which forms
it. Stress relief indentation 14 formed by the heated platen member
is, for reasons which are not entirely clear, likewise circular in
cross-section, although the radius of curvature of indentation 14
is generally slightly less than the radius of curvature of
indentation 12. Stress relief indentations 12 and 14 are further
characterized by the removal of thermoplastic material at the score
line without any corresponding buildup of material along the edges
16, 17, 18 and 19 of the indentations. This evidences the observed
fact that the heat-scoring process of the present invention is not
accompanied by undesirable lateral flow displacement of plastic
material away from the site of indentation.
Referring to FIG. 5, the invention is illustrated in the formation
of a box blank 15 provided with side panels 21, 22, 23 and 24, and
with a securing flap 25. End flaps 26 and 27 are formed on opposite
ends of panel 22; end flaps 28 and 29 are formed on opposite ends
of panel 24. Closure flap 30 with sealing wing 31 is provided on
panel 23, and a similar closure flap 34 with sealing wing 35 is
provided on panel 21.
A suitable die and platen arrangement for forming the box blank 15
is illustrated in FIGS. 6, 7 and 8.
Referring to FIGS. 6 and 7, the platen 40 is formed with heated
ridges 42 aligned with the scoring blades 48 of the die. Together
the heated ridges 42 and heated scoring blades 48 form the stress
relief indentations on opposite faces of the material along the
score line. As illustrated in FIGS. 6 and 8, it has been found that
satisfactory results can be obtained by forming the ridges 42 using
a plurality of heat-retaining steel tapes on the surface of the
platen 40 aligned with the scoring blades 48, and underlying the
lower surface of the material where scores 14 are to be formed.
Thus, by arranging a plurality of steel tapes 42 with a thickness
of about 0.015 inch and from about 1/8 to 1/4 inch in width, die
costs can be reduced, since the heat required to produce the lower
indentations 14 can be obtained, prior to feeding the material into
the press, by bringing the heated scoring blades 48 against the
steel tapes 42, which act as heat sinks, retaining sufficient heat
so that the sheet plastic between the die and the platen is
deformed on both the upper and lower surfaces thereof to form and
anneal the indentations 12 and 14 as illustrated in FIG. 1.
Referring to FIG. 7, the die 45 is provided with cutting blades 47
denoted by single lines and shown in elevation in FIG. 8, and
scoring blades 48 denoted by double lines shown in elevation in
FIG. 8. As will be understood by those skilled in the art, the
cutting blades 47 are formed with a sharp edge, as opposed to the
relatively blunted, preferably semi-circular edge of the scoring
blades 48. The cutting blades 47 are arranged to extend from the
die 45 a distance greater than the extension of scoring blades 48
from the die. With a 10 mil-thick (i.e., 0.010 inch) material, for
example, it is found desirable to set the cutting blades 47 to
extend 5 mils beyond the scoring blades 48, so that the sheet
material will be pierced by the cutting blades, with the scoring
blades compressing the material between the scoring blade 48 and
the tapes 42 to a thickness of 5 mils. Although ideally, the width
of the scoring blades 48 and the width of the tapes 42 should be
the same, it has been found that satisfactory results can be
obtained and alignment problems mimimized by utilizing a relatively
thin scoring blade bearing against a tape of considerably greater
width.
It is preferred that the cutting blades 47 be unheated as shown,
since cold cutting is found to provide a smoother edge.
Referring to FIG. 8, the elements of which are not necessarily
drawn to scale, the die 45 is formed with a cover plate 46 and a
phenolic asbestos insulation plate 49 arranged over nichrome wired
electrical heating element 51. Heating element 51 is supplied with
electric current in a conventional manner (not shown) and is
insulated from cutting blades 47 and in heat-exchange relationship
with scoring blades 48 which are supported by two sandwiched layers
52 and 53 of phenolic asbestos. Compressible rubber cushion members
54, when placed on the cutting blades 47 and on at least some of
the scoring blades 48, have been found to improve operations by
increasing heat retention in the scoring blades, by facilitating
separation of the plastic sheet material from the scoring and
cutting blades, and by preventing distortion of the plastic sheet
material during scoring. Desirably, the compressible rubber cushion
members are of 30 to 40 durometer hardness and extend about
one-sixteenth inch beyond the cutting blades 47 and scoring blades
48. As will be understood by those skilled in the art, the
aforementioned difference in extension of the cutting blades 47 and
scoring blades 48 is modified where the rubber
cushioning-insulating members 54 are employed. Preferably, the
blades are set to ensure formation of indentations 12 and 14 the
combined depth of which is between about 25 and 75 percent of the
thickness of the plastic sheet material. The sandwiched elements of
die assembly 45 are held in place by chase 55 during actual
operation.
DESCRIPTION OF PREFERRED EMBODIMENTS
The following examples are presented for the purpose of
illustrating, without limitation, the process, product and
apparatus of the present invention. In the examples, satisfactory
operation has been obtained on a 1260 Bobst press manufactured by
Bobst Machine Works, Lucerne, Switzerland, modified in accordance
with the present invention.
EXAMPLE I Material Poly(vinyl chloride) Thickness 10 mils Heater
temperature 250.degree.F. Score blade temperature 150.degree.F.
Blade pressure 90 lbs. per linear inch EXAMPLE II Material
Polycarbonate Thickness 10 mils Heater temperature 375.degree.F.
Score blade temperature 275.degree.F. Blade pressure 90 lbs. per
linear inch EXAMPLE III Material Polyester Thickness 10 mils Heater
temperature 300.degree.F. Score blade temperature 200.degree.F.
Blade pressure 90 lbs. per linear inch
The foregoing disclosure and examples have been given for purposes
of illustration and elucidation, and not by way of limitation. It
is understood that changes and variations can be made without
departing from the scope of the invention as defined in the
following claims.
* * * * *