CA1169750A

CA1169750A - Postformable laminates

Info

Publication number: CA1169750A
Application number: CA000386784A
Authority: CA
Inventors: Edward B. Hussey; John R. Wood
Original assignee: Domtar Inc
Current assignee: PANOLAM INDUSTRIES Ltd
Priority date: 1981-09-28
Filing date: 1981-09-28
Publication date: 1984-06-26

Abstract

POSTFORMABLE LAMINATES
ABSTRACT
A postformable decorative high pressure laminate is formed by a facing sheet and a plurality of core sheets, including a backing sheet; the backing sheet is modified to structurally weaken the sheet and thereby to improve its extensibility by lines of weakness formed in the backing sheet in the area of the laminate to be postformed.

Description

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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 ~ 2 -.

s~ 69 (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.

-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 , 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 , -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 ,'~'~ 5~
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.

Claims

1. A postformable high pressure decorative laminate comprising a top sheet and a plurality of paper core sheets, the farthest of the latter from the front sheet forming a paper back sheet, all of said sheets being impregnated with thermo-setting resin, means of modifying said back sheet to structually weaken the same to improve its extensibility in an area of a bend to be formed in the laminate by postforming, said modifying means comprising spaced apart score lines of weakness form in said paper back sheet, each score line extending continu-ously through the bend to be formed in the laminate, each score line extending at an angle between 10 and 75° to the direction of the axis of curvature of the bend.

2. A postformable high pressure laminate as defined in claim 1 wherein the score lines are made of a plurality of laterally spaced apart slits through said paper back sheet, said slits extending at an angle of between 10 and 75° to the axis of curvature of the bend to be performed in said laminate.

3. A laminate as defined in claim 1 wherein said score lines are laterally spaced apart no greater than one-quarter of an inch.

4. A laminate as defined in claims 2 or 3 wherein said angle is between 20 and 45° and the paper back sheet is made of a kraft paper sheet.

5. A laminate as defined in claim 1 wherein said score lines of weakness are formed by scoring the paper back sheet after consolidation.

6. A laminate as defined in claim 5 wherein said lines extend at an angle of 10 to 75° to the axis of curvature of a bend to be applied to said laminate when said laminate is postformed in said area.

7. A laminate as defined in claim 6 wherein said score lines are spaced no greater than one quarter of an inch apart measured in a direction perpendicular to said lines.

8. A laminate as defined in claims 6 or 7 wherein said angle is between 20 and 45°.

9. A laminate as defined in claim 1 wherein each score line extends slightly past each side of the bend to be formed in the laminate.