Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Field of the Inven~ion
.
The present invention relates to postformable
laminates, more particulArly to postformable high pr~ssure
l~minates.
Backqround o~ the Inventlon
Generally, the high pressure decorative laminate
is composed of a plurality of core sheets impregnated with a
phenol-formaldehyde resin which are covered by a decorative
sheet such as a decorative print sheet impregnated with a
melamine-~ormaldehyde resin~ The cover sheet may in turn be
covered by a protective overlay sheet of an alpha-cellulose
type paper impregnated with melamine-formaldehyde resin.
Decorative laminates are used for many pplica-
tions, including des~ tops or kitchen or bathroom counters,
etc. and in many such applications require shaping (yeneral-
ly bendin~) after the laminate has been pressed and cured~
Consolida~ed laminates capable of being shaped are generally
referred to as postformable laminates and include the basic
layups described hereinabove for high pressure laminates but
with the bottom sheet (the sheet at the opposite side of the
laminate from the cover or overlay sheet) of a crepe paper
to provide the required extensibility to permit the laminate
to be formed. Other special extensible papers such as
papers sold ur.der the trademark Clupak are also used and in
some cases more than one such paper is used depending on the
quali.y and the thickness of the postformable laminate.
In mar.y cases, the resins used to impregnate the
sheets of the lay-ups are modified to facilitate post
forming and/or the curing cycle is adjusted to improve post
~0 ~orm2bility.
The crepe paper is relatively expensive since it
has to ke creped in .wo different directions to obtain
stretch in ihe transv~rse or cross ~.achine di ection
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(generally X~creping, su~h paper bein~ sold by Cindus ~us-
tries Cincinati Ohio). Similarly, the other special exten-
sible papers are significantly more expensive th~n Kraft
paper.
rief Description of the Invention
It is the object of the present invention to
replace the X-crepe backing sheet with a conventional kraft
sheet modified to provide the required stretch characteris-
tics.
Broadly, the present inven~ion ~elates to a post-
formable high pressure laminate formed from a top sheet and
a plurality of paper core sheets impregnated with thermo setting
resin and having a paper back sheet structurally modiied to
weaken same to facilitate extension thereof at least over
the area of the laminate to be postformed by facilitating
local deformation of the backing sheet. The modification is
provided by a plurali~y of ~G~re lines of wea~;ness.in s~id back
sheet, said lines traversing the area to be postformed and
extending beyond the postformed area on each side hereof by
20 a distance of at least 1/8 inch and being spaced apart less
than 1/4" measured in the direction perpendicular to the
lines.
Brief Descr tion of the Drawings
Further features, objects and advantages will be
evident from the following detailed description of the pre-
ferred embodiments of the present invention taken in con-
junction witA the accompanying~drawing, in which:
. Fisure 1 is an enlarged partial isometric view illus-
trating a laminate incorporating one form of the present
invention~
Figure ~ is an enlarged c~oss-section to an inside
corner formed in a laminate constructed in accordance with the
present invention.
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Deta,led Descrip,ion of the PreFer-ed Embodiment
As shown in Fisure 1, the laminate 10 includes a
core formed by a plurality of layers of thermo-settinq resin
impregnated ~kraft) paper sheets bonded together under heat and
pressure. A decorative surface is normally provided on the
laminate and is formed by a decorative covering sheet
impregnated with a thermo setting resin and may, if desired
be cove_ed by an alpha cellulose overlay sheet impregnated
with thermo-setting resin. This whole assembly is secured
together by setting of the resins impregnating the core,
cover and overlay sheets under heat and pressure condi-
tions. In the illustrated arrangement the decorative
surface is indicated by the numeral 12 and back sheet by the
numeral 14.
The back sheet 14 at least in the area to be post-
formed is locally modified structurally to provide the
required extensibility. This strutural modification is pro-
vided by a plurality of substantially parallel score 1-ines of
weakness 16. These lines of weakness 16 are spaced ~part in
~0 the direction perpendicular to the lines 16 a distance S to
provide bands 1~. It has been found that the distance S
should not exceed 1/4~ if relatively sharp (small radius
e.g. 3/16") bends are to be applied with the d~corative
surface forming the inside of the curve. Obviously, the
minimum radius ~ill de~end on the make up of the laminate
and to some ex~ent on the angle ~ of the lines 16 to the
axis of curvature and the degree oF wea~ening of backing
sheet by lines 16 as will be described hereinbelo~.
In the illustrated arrangement, the centre or
axis of curvature of the bend of radius R to be applied to
the laminate by post-forming is indicated by the line A-A in
Figu~es 1 and 2. The lines 16 extended in an angle to this
axis A-~ of ~ degrees.
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It is ~elieved ~ha' the extensibili~y is provided
by opening of the lin~ o' weakness and ~he angle 4, it has
been found, must be ir. the range of about 10 to 75, more
generally in a range of about 20 to 45 and preferably about
.
The length of the lines 16 is designated as the
length of the line measured in the direction perpendicular
to the axis of t~e curvature i.e. to the axis A-A and is
indicated by the let~er L in Figures 1 and 2. The lines 16
~or bands 15) should extend beyond the curve section as
indicated at 1.~ in Figure 2 and into he tangentially
extending sectionQ 20 and 22 on o~posite sides of the curved
section 18. ~lhe distance that the slits 16 (or bands 15)
must extend into the tangential sections 20 and 22 may be
varied depending on the radius R, However, it is generally
preferred that for the short radius bands ~3/16 in radius)
which are those that enco~nter the greatest difficulty and
necessitate the use of the present invention or some other
means such as the crepe sheet, that the lines extend a mini-
mum of 1/8 in and generally greater than 1/4 in on each sideof the curve section 18 ~the length is also influenced ~o
some degree by the spacing 5). Obviously, there is no
necessity to make the lines 16 any longer than necesary,
since ~xtra length simply increases the cost of producing
the slits. However, it is desirable to make these lines
significantly longer to provide flexibilty in alignin~ the
axis A-A in ~roper position within the length 3f the lines,
i.e. the axis A-A need not fall in the centre of the length
L, it being on~y necessary that the lines 16 extend at least
the minlmum distance on each side or the curve.
The lines 1~ may be ~pplied t~ the backing sheet 14
be,~ore the lamin2~ing layup is made up i.e. before tbe resin
is cured. For exa~ple, on the sheeter forming the
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imp egnated web into discrete sheets ~nd then fed into thepress as part of ~he layup. Alternativel~l, the lines 16 may
be forme~ in the backing sheet after consolidation e . g.
during or after sandins e.g. by scoring or otherwise
mechanically weakening. Generally for the lines 16 to be
applied to the ba~kin~ sheet before making the la~up the
lines will be in the form of slits ex~ending righ~ through
the sheet. In the preferred formation, the lines will be
applied after consolidation i.e. during or after sanding.
The lines 16 must be sufficiently deep to weaken the shset
so that it may be expanded without cracking of the sheet to
render the postformed laminate unacceptable and yet not so
deep as to result in show through of the lines after expension.
For some reason weakening by scoring in the full depth of
score of the backing paper sheets contributes to show through
whereas slitting before laminating, the spacing of, and the
angle of the slits seem to be the major factors contributing
to show throlgh. The depth of score may vary with spacing
S (the wider the spacing S generally the deeper the lines
16 must be scored) an angle ~ of 30 seems to require the
minimum depth of score. In any event, the scores or lines
16 will normally have a depth of at least .003 inches and
preferably about .005 to .010 inches. The term -score-- or
scoring as used herein means a line formed by cutting the
fibres opposed to an indentation of the slit by bending the
fibres which will not operate.
In a conventional multi-opening press, the layup
is formed by decorative and surface sheet or sheets, a
plurality of core sheets including a back sheet with a
separator sheet (generally glassine paper) separating the
back sheet from the back sheet of another larninating layup
arranged ln back to back relationship as a mirror image wjth
the one described. The decorative surface sheets of each
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layup is pressed in ~ace-to-face relationship with a
suitable caul plate and the layups and caul plates so
arranged are inserted into the press.
Example 1
A plurality of tests were carried out using
backing sheets pre slit before laminating (i.e. tne line 16
- being formed by slits though the backing sheet) and having
different slitting angles 4 for a spacing S=1/8 inch. The
laminates were tested in the lab according to Canadian
Standard Test Method No. 5.12 CAN3-A172-M79 by forming
around 3/16 inch radius blocks at a temperature of 155C.
Tests at angle ~ of 10, 20, 60 and 7S indicated that
satisfactorty products could be produced at any of these
angles, however, at opposite ends of this angular scale
i.e. the 10 and 60 and 75 the laminates showed some signs
of crackins indicating the extremes of the range for R=3/16
inches.
When the slit spacing S with the slits at an angle
5} of 30 was increased to about 1/4 inch i.e. S = 1/4 inch,
the laminate could not be formed satisfactorily to the 3/16
inch curvature at a temperature of 155C. However, at
spacing S below 1/4 inch down to l/16 inch no problems were
encountered. Less than about 1/16 inch spacing simply
increase the slitting operation without a significant
advantageous effect and thus it is preferred to have S equal
between about 1/8 inch and ~/16 inch.
It will be apparent that the u~e of slits as above
described provides an adequate means for increasing the
`: extensibility of the back sheet to permit forming and pro-
vide a commercially acceptable postformable laminate.
In the above example, the slits are extended riyht
through the paper and have been applied prior to the
laminating step. As above indicated, it is also possible to
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attain a similar result by not slitting completely through
the paper but by scoring e.g. by scribing with a sharp
instrument subsequent to the consolidation step wherein the
laminate is consolidated and th~ resin cured.
Example 2
A plurality Of laminates were consolidated and
their back or rear faces sanded in the conventional manner
and then scored by a sharp scribe to form lines of weakness
penetrating partly through the backing sheet. As above
indicated, the lines are cut in the sheet with a minimum of
compression since compressing the sheets along the lines 16
will normally result in show through on the upper face.
The slit spacing S was 1/8 inch and the depth of
score was varied between .004 inch and 0.01 inch and the
angle 4 was for 30 and 60~. It was found that within the
above ranges satifactory post forming was attained con-
sistently. However, at depths of .010 inch with the scoring
tool used the score lines were becoming visible (showed
through) on the face side of the laminate. When the angle 4
was changed to 60 the minimum depth of score had to be
increased to about .08 inch to obtain satisfactory post
iorming. ~he following table summarizes the results.
ScoreAngle Spacing Results
Depth 4 S
InchDe~ree Inch
_
0.004 30 1/8 Satisfactory formability
0.006 30 1/8 Good formability
0.008 30 1/8 Good formability
0.010 30 1/8 Excellent formability
(some show through)
0.006 60 1/8 Unsatisfactory
0.008 60 1/8 Satisfactory formability
0.010 60 1/8 Good formability
0.008 60 1/4 Poor formability
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The thickness of each of the laminates ~ested in
Examples 1 & 2 was about 0.03 to about 0.032 inches and each
laminate co~lprise five layers (the kraft lay~rs generally
being thicker than the top or cover sheet). Most post-
formable laminates have a thickness in the range of about
0.02~ to abou~ 0.05 lnches and thus if the thickness af the
laminate to be produced deviates from the about 0.03 inch
thickness of Examples, the effective depth of the score may
have to be changed slightly. Generally, the depth of the
score will be about equal to the thickness of one of the
kraft sheets after consolidation into the laminate.
The type of scoring tool used i.e. one that cuts
material versus abrasion versus displacement (plowing) and
the type of resins and forming conditions, and relative
speed of the tool to the laminate may change the range of
depth of score that will be effective. The scoring tool
used in table 1 cut material from the laminate.
In all of the illustrated arrangements the
weakening has been shown as applied in discrete local areas,
but in some cases it may be desirable to provide the lines
of weakness over substantially the whole area of the sheet
so that the post-forming may be performed at any location
across the sheet i.e. when it is not preknown where the
sheet is likely to be post-formed.
It will be apparent from the above that the
present invention produces a postformable high pressure
laminate that does not incorporate a backing sheet or a
crepe paper.
Modifications may be made without departing from
the spirit of the invention as defined in the appended
claims.
