CA2085789C - Miter-foldable saturated paper-based overlay system and method for fabricating the same - Google Patents

Abstract

A paper sheet is saturated with a latex saturant wherein two components have different Tg values to produce an overlay which sufficiently resists the stresses of miter-folding, or V-grooving, and possesses superior printing qualities which favor its application on substrates such as miter-folded boards and particle boards, cabinetry, shelves, furniture, intricate surfaces such as profile wraps and molding strips, doors, frames, and other such structures.

Description

FIELD OF THE INVENTION

The present invention relates to laminates and overlays, and more particularly to a miter-foldable saturated paper-based overlay system and method for fabricating the same.

BACKGROUND OF THE INVENTION

Decorative vinyl laminates are a recognized alternative to natural woods in furniture manufacturing and woodworking because they provide abrasion resistance, scratch resistance, water resistance, chemical resistance, barrier performance and flame spread resistance. Adhesive technology has advanced to the extent that various epoxy, emulsion and solvent adhesives are available to bond the vinyl laminates to the substrate, depending upon the desired application.
However, notwithstanding their physical properties, vinyl laminates have high elongation which result in a poor printed appearance. A typical vinyl product has two plies, a solid color base (color throughout) that is printed, and a clear vinyl that is laminated over the print to protect it from abuse. The clear film is often coated with a scratch-resistant coating to enhance its protective properties. Vinyl has a poor appearance when printed because it stretches in the printing press and thereby "smears" the image.

20857~9 It would be deslrable to use paper instead of vinyl because of the superior print quality and the manageability of paper during lam~natlon. However, papers lack the physical strength required of machinable materlals. Particularly, in miter-fold applicatlons wherein an overlay materlal (vlnyl) is glued to one side of a partlcle board which is cut on the opposite side w~th V-grooves and then bent at those grooves to form corners and angles, paper would have to possess strength sufflcient to resist tearing and/or splitting when the miter-fold edge is formed.
Until the instant invention, the superior printing quality of paper could not be exploited in miter-fold appllcations because of the severe stresses encountered during the miter-folding or "V-grooving"
operation. In view of the disadvantages of the prior art vinyl laminate overlays, novel paper-based overlay systems are needed.

2~5789 SUHMARr OF THE INVENTION
The present invention provides a paper-based overlay system which comprises the use of a saturated paper having sufficient "miter-fold" strength, adequate smoothness for printers, and adequate adhesive anchorage capab~lities for application to surface structures. A
method for making the overlay system is also disclosed.
A paper sheet is saturated with a saturant comprising a latex having at least two components with different Tg values to produce an overlay which sufficiently resists the stresses of miter-folding, also called "V-grooving", and possesses superior printing qualities which favor its application on substrates such as miter-folded boards and particle boards, cabinetry, shelves, furniture, ~ntricate surfaces such as profile wraps and molding strips, doors, frames, and other such substrates which may or may not be formed by m~ter-cutting/folding.
In an exemplary saturated paper-based overlay, a sheet of paper is saturated with an acrylic/PVC blend and hot calendered to a hlgh degree of smoothness.
Optionally, a thickener, such as sodium alginate, is added to the saturant to reduce surface migration of the lower Tg component, and a release agent, such as sorbitan tristearate, is added to prevent the material from sticking during calendering. The sheet may be colored, printed, imaged, and/or patterned, such as by rotogravure processes, and applied to one or more surfaces of a substrate.
Overlaid substrates of the invention comprise the use of the saturated paper sheet on a substrate such as a board. The board may be miter-cut on at least one surface and folded such that a continuous paper surface ~s presented at the miter-folded edge.

208~789 Other overlaid substrates include hlghly detailed surfaces such as moldings and frames which have intricate surfaces that may or may not involve miter-cutting and folding but which nevertheless impose stresses by v~rtue of the forces imposed on the paper by the sharp grooves, angles, or detailing in the profile wrapping.
The overlaid substrates of the inventlon may therefore include cabinets, shelves, drawers, enclosures, tabletops, doors, frames, molding, and the like, which have saturated paper overlay adhered to at least two non-coplanar surfaces.
A method for fabricating the overlay comprises the step of saturating a paper sheet in a saturant system comprising at least two components hav~ng different Tg values. The saturated sheet is preferably stack-calendered to obtain a uniform caliper and smoothness, and optionally printed, colored, imaged, and/or patterned, either before or after application to boards or other surfaces. The method may further compr~se the step of adhering the saturated paper sheet to at least one surface of a substrate which is miter-cut and folded to present a continuous paper surface along the miter-folded cut.
A method for fabricating profile wrapping or highly-detailed substrates overlaid with the saturated paper-based overlay compr~ses the step of providing a highly irregular surface and adhering the paper-based overlay contiguously with the surface. In an exemplary method, the paper ~s patterned with wood grain, and the patterned paper is applied to a substrate surface to create an appearance that the substrate or structure is comprlsed of solld wood.

208578~

BRIEF DESCRIPTION ~F THE INYE TION
Flg. 1 is a dlagrammatlc view of a threadlng system for the stack calender used ln accordance wlth the present invent~on;
Flg. 2 is an lllustratlve comparison of ~mportant properties of paper and vinyl for overlay applications;
Fig. 3 is a plan side-view of a saturated paper-based overlay of the lnventlon appl~ed to a substrate such as a board or structure;
F~g. 4 ls a plan slde vlew of the overlay-covered substrate of Fig. 3 whereln the other surface of the substrate has been mlter-cut;
Fig. 5 is a plan slde vlew of the miter-cut board of Fig. 4 folded along mlter cuts;
Fig. 6 is a plan vlew of an enclosure formed by foldlng together the miter-cut sectlons of the board shown ~n Fig. 5;
Fig. 7 is a perspective illustratlon of ganged saws for s~multaneous miter cuttlng;
F~g. 8 is a side lllustrative view of an exemplary overlay system comprising a substrate havlng a paper-based overlay; and F~g. 9 is a slde cross-sectional view of a substrate, such as a decoratlve molding strip, wh~ch has a detailed surface upon which a saturated paper-based overlay ls adhered.

DETAILED DESCRIPTION OF THE INVENTION
The invention comprises a saturated paper-based overlay system, including overlaid substrates (or structures), and methods for fabricating the same. As used herein, the term "substrate" means and refers to structures, materials, and/or objects.
The overlay system of the invention comprises a paper sheet, preferably of heavy weight paper, that has been saturated with a latex saturant having at least two components with different glass transition (Tg) values.
An exemplary saturant comprises a latex blend of (1) acrylic, which has a Tg of about -10; and (2) unplasticized polyvinyl chloride (PVC), which has a Tg of about +67. Although less preferred, ethylene vlnyl acetate (EVA) can be substituted for the acrylic.
EVA also has a Tg of about -10. Styrene acrylate, vinyl acetate, or methyl methacrylate may be substituted for or added in combination with the PVC. Preferably, the Tg of one of the latex components is such that at room temperature the component does not tend to form a film.
Preferably, the Tg of the saturant components d~ffer by 30. More preferably, the difference is at least 40, and most preferably it is greater than 50.
For example, the acryllc/PVC blend has Tg values which differ by 70. It is believed that the acrylic functions as a binder which sets around or upon the cellulosic fibers of the paper and the PVC latex particles which do not form a film but remain for the most part as individual particles; and that the PVC particles, d~stributed about the cellulosic matrix, are then melted, such as during calenderlng, and hold the system together in a denser matrix than would the acrylic acting alone.

20~5789 _ Suitable raw paper for use in the instant invention must have good formation and good physical strength, and must be saturable. The preferred raw paper meeting these requirements is Owensboro HP-8 75#
available from W.R. Grace & Co.-Conn. Such paper has a fiber composition of 85% (by weight) Northern Bleached Softwood Kraft and 15% (by weight) Hemlock Sulfite.
Preferably, the paper is of a heavy weight, and the cellosic fibers which constitute the paper are random, such that the paper sheet has machine direction (MD) and cross direction (CD) strength; in other words, it is strong in many directions, although it is not necessary that it be equally strong in all directions.
The saturant system must be able to withstand the actual physical abuse delivered to the sheet during a V-grooving operation. The physical properties that relate best to this operation are, in the order of importance, edge tear and tear initiation, internal tear (tear propagation), delamination resistance, and tensile strength/elongation. In addition, the saturant system must have the ability to be calendered to a high degree of smoothness, and must maintain that smoothness. An immediate smoothness less than about 100 Sheffield units is preferred.
An acrylic system, being plastic by nature, calenders to the required smoothness. Acrylics are also lightfast, which is a further advantage of the saturant.
Preferably, an acrylic latex such as HYCAR~ 26104 available from The B.F. Goodrich Chemical Company, i s suitable for use in the invention. The acrvlic latex can be used in an amount of from 55% to 96.75%, and preferably 55-667., most preferably about 56.75%, on a dry basis, depending upon the processing and smoothness retentlon.

Wh~le lnorganic fillers may be used in the saturant system, such as clay or titanium dioxide, these tend to cause failures during miter-foldlng. Organic fillers such as unplasticized PVC are less destructive to the cellulose fibers during miter-folding because the particles are spherical rather than platelet-shaped and are believed to be less damaging to the strength of the cellosic fibers in comparison with the inorganic fillers. A suitable PVC latex is GEON~ 352, available from B.F. Goodrich, which is used in an amount of from OX to 40Z, preferably 33-40%, and most preferably about 40X, on a dry basis. An ethylene vinyl acetate ~EVA), such as Dur-O-Set~ E-646, available from the National Starch Company, may be used instead of the acrylic.
In order to increase the delamination resistance of the overlay, it is necessary to reduce the level of binder migration common during the drying of heavyweight papers. ~ thickener can be added to the saturant system for this purpose. Known cellulosic thickeners can be used. Sodium polyacrylate and alkali reactive emulsions can also be used. However, cellulosics impart solvent resistance to the saturant (which can interfere with printabiliy), and brittleness. Sodium polyacrylate and the alkali reactive emulsions also exhibit these effects and can be water sensitive as well. Accordingly, the preferred thickener is sodium alginate. Kelgin~ MV, available from Kelco, Inc., may be used in an amount of from 0.15X to 0.35X, dry basis, to limit migration at Yar jOU5 saturator line speeds.

208S7~J

g Another functional ingredient for the saturant system ls a release agent, whlch is belleved to mlgrate to the surface of the sheet durlng the calenderlng operation and provlde release from the hot steel rolls.
Emulsifled waxes or waxy materlals could be used for this purpose, although emulsified waxes tend to cause smoke generation during processlng. Waxy materials such as stearylated melamine can impart other propert~es that may or may not be undesirable, such as water res~stance after processlng. Preferably, the release agent is sorbitan trlstearate, such as T~EEN~ 65 from ICI
Americas, Inc. Sorbltan tristearate also can be used to lmprove smoothness. It ~s used in an amount of from 0%
to 3% on a dry basis to provide release from the hot calender rolls at varlous calender llne speeds.
Other lnert ingredients, such as pigments and defoamers can be added. Preferably, the paper ls saturated to a 40X add-on level.
An exemplary saturant system comprises the following amounts of preferred ~ngredlents on a dry sol~ds bas~s:

56.75% acrylic latex 40.00% polyvinyl chloride latex 0.25% sodlum alginate 3.00Z sorbitan tristearate S1nce the pH of acryllc latexes ls generally low, and the pH of PVC latexes is generally high. it is preferred that the pH of the acryllc latex be rai;ed w~th dilute ammonium hydroxide and that the PVC latex be added thereto slowly. The order of addltion of the remainlng ingredients is not crltical.

1 o Fig. 1 illustrates an exemplary procedure for fabricating an exemplary saturated paper-based overlay in accordance with the instant invention. The paper is unwound from roll 1, and passed by tension transducer roll 2 to heated steel calender roll 4. The paper then travels through a nip formed between roll 4 and fiber calender roll 5, past mt. hope spreader roll 6, tension rolls 3 and 3' (turned off and used as idler rolls~, idler roll 7, and a eecond heated steel ca',ender roll 8 and fiber calender roll 5. The sheet then passes over a steel idler roll 9, and is cooled by first and second cooling rolls 10 and 11. Adequate heat transfer between the paper web and these cooling rolls can be accomplished by cooling the rolls with ordinary tap water, which is typically at temperatures from 58F to 72~F, most typically 65F. The sheet then passes over a large diameter mt. hope roll 12 and a large diameter ~dler roll 13, and is rewound on roll 14. The practical m~nimum diameter of any of the rolls is about 3 inches.
The saturator squeeze rolls (not shown) and the calender steel rolls must be of a diameter and construction that will resist flexing while in operation. The m~nimum diameter of any of the rolls is 3 inches.
Temperature of the heated calender rolls, line speed and nip pressure are cr~tical ~n order to aehieve uniform caliper and smoothness of the sheet. It is preferred that the line speed be 150 feet/minute, that the nip pressure be 1100 psig, and that the temperature of the heated steel calender rolls a and 8 be 325F.
Sign1ficant deviations from these values may re5ult in a product that is unstable in terms of smoothness.

.. X. 1 _ 20857~9 66925-509 EXA~PLE 1 A comparlson of some of the properties of paper and 8 mil vinyl sandwlch film is shown ln Fig. 2. The vinyl sandwich film compared therein was produced in accordance wlth the process outllned ln PLASTIC FILMS, second edition, by John H. Briston, chapter 8, section 2, 1983.
In particular, the sandwich film is two films, one colored and prlnted, and the other clear, that are laminated together. Both of the films of thls sandwich were made by the process outlined in section 8.2.
The saturated paper of Figure 2 was made in accordance wlth the lnstant lnvention. The untreated paper was saturated by forcinq the paper to enter a large shallow pan containing the saturant mixture. The paper was then d~rected through a pa~r of squeeze rolls. The squeez~ng or wrlnglng of the paper controls the add-on level. After squeez~ng, the paper was dried by a combination of forced hot-air, infrared and contact heat dryers. The paper was saturated to a 40X add-on level. Once dry, the paper was rerolled and subjected to the calendering process in accordance with the lnstant ~nventlon.

208~789 Figure 2 shows the signif~cant advantages of uslng paper instead of vinyl ~n terms of percent elongat~on and Elmendorf tear (grams), w~thout sacr~f~c~ng tensile strength (lbs/inch of w~dth). The saturated paper does not stretch much in terms of percentage elongat~on, and therefore reta~ns better printing reglstration. However, the tear propert~es for the paper are still high enough for adequate performance in m~terfold applicat~ons. Preferably the saturated paper used in accordance with the instant invention has a caliper of 6-8 mils and a Sheffield smoothness of about 8~.
In further exemplary paper-based overlays of the invention, the saturated paper sheet is preferably printed, colored, patterned, and/or imaged. The paper overlays are compatible with nltrocellulose based ~nks and pa~nts, polyurethane based ~nks and paints, and even vinylic inks and paints. The papers may be ~maged or patterned us~ng any known process, such as by rotogravure processes which are often used by furn~ture manufacturers to impart a woodgrain look. The papers may also be colored with known ~nks or paints. In other exemplary overlays, a protective coating may be applied prior to or after ~nstallat~on of the paper to a substrate surface. Most preferred are polyurethane coatings and varnishes.

Exemplary saturated paper-based overlay systems of the lnvention comprlse (1) a paper sheet saturated wlth at least two latex components havlng dlfferent Tg values and hot-calendered; and (2) a structure havlng at least one surface upon which said saturated paper sheet is adhered. Accordlngly, the system comprlses a sheet of paper saturated ln a latex saturant comprlslng at least two latex components, the flrst of said latex components lncludlng acryllc or ethylene vlnyl acetate, and the second of said latex components ~ncludlng polyvlnyl chlorlde, styrene acrylate, vlnyl acetate, or methyl methacrylate, said sheet belng calendered after saturatlon; and a substrate havlng a surface for dlsposltlon thereupon of sald saturated paper sheet, whereby said paper sheet covers at least a portlon of sald substrate. The substrate may further comprise ~oined non-planar surfaces, such as a mlter-folded corner, across whlch the saturated paper is adhered as a contlnuous, coherent sheet.
Flgs. 3-6 lllustrate a method for fabrlcatlng an exemplary saturated paper-based overlay system whereln the saturated paper sheet 28 ls adhered onto a flrst side or surface 26 of a substrate such as a board 20 or other surface structure. The adhesive 26 may be first applled to the board 20 surface 22 or to the paper sheet 28 (Fig. 3). Mlter cuts 30 are made on the second or opposlte side 24 of the board 20 to form separate sectlons 30 (Fig. 4) whlch are then folded or joined at the mlter cuts 30 (See Flg. 5~ to form the desired object 34 such as a box 34. Cabinets, drawers, frames, tabletops, doors, enclosures, speaker enclosures, and other ob~ects may be fabricated using the saturated paper 28, which wlthstands the stresses of mlter-cuttlng 30 and foldlng (Flg. 5) so as to present a contlnuous sheet of paper at mlter-folded edges 29.

- -20~5789 _ Known adhesives 26 may be used, such as urea formladehyde, polyvinyl acetate, ethylene vinyl acetate (EVA), or epoxies. The use of EVAs are preferred.
Fig. 7 illustrates the use of ganged saws 36 for simultaneously miter-cutt~ng a number of grooves 30 at once in a substrate such as a particle board 20. The board has a saturated paper-based overlay 28 adhered on a ma~or face. The paper overlay 28 may also be adhered on minor faces 20b to provide a continuous appearance when the ma~or and minor faces are simultaneously viewed. The arrow 35 indicates a direction across the mitercuts 30 for cutting a channel or groove (dotted line) for containing a face plate or other surface between the sides 20b when folded together.
As shown in Fig. 8, the saturated paper 28 may be applied to a board 20, such as a particle, laminate, or composite board, whlch has been miter-cut 30 at more than one point on the board 28. The various miter cuts 30 may be variously angled and spaced from each other such that an infinite variety of overlaid structures can be fabricated. Accordingly, the saturated paper-based overlay system of the invention is sufficiently strong that the paper may be applied to a structure which is subjected to numerous miter folds 30 which impose a large cumulative stress to the coherent paper overlay 28, which nevertheless provides a continuous surface 29 at the folds 30.
The saturated paper-based system of the invention may also include a substrate that is a decorative mo1ding or strip, as shown in the cross-,ec~ional vi~w at 35, which may or may not be miter-cut but which presents irregularities and at least two surfaces which are not co-planar. Such intricate surfaces may seriously challenge the successful application of decorative laminates.

Accord~ngly, an exemplary overlay system compr~ses such a structure 35 as shown ~n Fig. 9 wh~ch has a high degree of deta~l~ng, ~e. varlous sharp edges, projections, ~ndentatlons, angles, and curves as ~ndicated generally at 36. The overlay 28 may be opt~onally colored, pr~nted, and/or patterned.
As mod~f~catlons may be ev~dent to those sk~lled ~n the art, the forego~ng embod~ments are ~llustrat~ve only, and the scope of the ~nvention ~s limited only by the claims.

Claims (19)

1. A paper-based overlay system, comprising:
a sheet of paper saturated in a latex saturant having two components with different Tg values.

2. The overlay system of claim 1 wherein the difference of said Tg values is at least 50.

3. The overlay system of claim 1 wherein at least one of said components does not form a film at room temperature.

4. The overlay system of claim 2 wherein said saturant comprises acrylic and polyvinyl chloride.

5. The overlay system of claim 2 wherein said saturant comprises a first component which includes acrylic or ethylene vinyl acetate, and a second component including polyvinyl chloride, styrene acrylate, vinyl acetate, or methyl methacrylate.

6. The overlay system of claim 5 wherein said saturant further comprises a thickener operative to thicken said saturant.

7. The overlay system of claim 6 wherein said saturant further comprises a release agent and said saturated paper is hot calendered.

8. The overlay system of claim 7 further comprising a substrate and a layer of adhesive, said substrate having at least one surface upon which said paper sheet is adhered by said adhesive layer.

9. The overlay system of claim 8 wherein said paper sheet further comprises a pattern.

10. The overlay system of claim 9 wherein said pattern is a wood-grain.

11. The overlay system of claim 8 wherein said sheet of paper further comprises a colorant.

12. The overlay system of claim 8 wherein said substrate has at least one edge over which said paper is disposed.

13. The overlay system of claim 12 wherein said edge is made by miterfolding.

14. A paper-based overlay system, comprising:
a sheet of paper saturated in a latex saturant comprising at least two latex components, the first of said latex components including acrylic or ethylene vinyl acetate, and the second of said latex components including polyvinyl chloride, styrene acrylate, vinyl acetate, or methyl methacrylate, said sheet being calendered after saturation; and a substrate having a surface for disposition thereupon of said saturated paper sheet, whereby said paper sheet covers at least a portion of said substrate.

15. The overlay system of claim 14 wherein said substrate is comprised of a board that has at least one edge upon which said saturated paper forms a continuous layer.

16. The overlay system of claim 15 wherein said edge is formed by miter-folding.

17. A method for fabricating a saturated paper-based overlay system, comprising the steps of:
providing a sheet of paper; and saturating said paper sheet in saturant comprising at least two components having different Tg values; and calendering said saturated sheet.

18. The method of claim 17 further comprising the step of patterning, imaging, or coloring said saturated sheet.

19. The method of claim 18 further comprising the step of adhering said sheet to a first face of a subsrate, miter-cutting a second face of said substrate, and folding said substrate along said miter-cut, whereby a continuous layer of said paper is presented along said fold.