CA1046183A - Embossable sheet material comprising a base sheet of a stress-whitening elastomer modified poly (methylmethyacrylate) - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
An embossing machine tape is provided employing a film of a stress whitening, substantially transparent elastomer-modified methyl methacrylate polymer, normally employed in combination with a non-stress whitening, opaque, normally colored, polymeric film backing. In usual applications, an adhesive coating is applied to the backing and protected by a releasable liner. The stress whiten-film provides sharply delineated symbols without fracture, when embossed, and substantially free of ghosts in the usual embodiment.

Description

BACKGROUND OF THE INVENTION
Field of the Invention Embo~ing tapoe find wide u~e. In the fabrication of many embo~ing tape~ tre~ whitening film i~ employed with a darkened bac~ground. By ~tre~s whitening it i~ intended to m0an the characteri~tic of a material that changes color and/or opacity, when ~ubjected to cold flow. In ~tre~ whitoning material~, the yield point occur~ at a low degree of elongation.
In embo~ing, it i~ desirable that the alpha-numeric 10 8ymbol becomes entirely opaque and white, 80 as to clearly ~tand out and be legible. The emboJ~ed symbol ~hould not fracture which destroys legibility and create~ an unacceptable appearance, should be froe of ghosting, which i~ un~ightly and affect~ legibility, and be able to retain the ~harp characteri~tic~ for long periods of time under varying condition~.
To some dogree, the ~tre~s whitening and fracturing of the ~ymbol8 is as~ociated. The stre~sing of the polymoric film by cold flow elongation, re~ults in changes in the phy~ical character-i~tics of the polymer, which make~ the film ~usceptible to fracture.
It i~ de~irable to find an embossing tape which provide~ a high degree of stre~s whitening or opacity, while being ~ub~tantially free of fracturing on embossing. Al~o, any film used for an embossing tape should be easily proces~ed and fabricated, readily adhere to a base film, and ke ~table or stabilizable to heat and light, ~o as to retain its characteristics for long periods of time.
escription of the Prior Art U.S. Patents 2,925,625, is~ued February 23, 1960 to Dymo Indu~tries, Inc.; 2,996,822, i9sued August 22~ 1961 toDy~0 ~ SIRj~SJ
Inc. 3,036,945, issued May 29, 1962 to Dymo Indu~trie~, Inc.: and 1046~83 3 42,630 i~0ued November 24, 1970 to Dymo Indu~triea, Inc. dioclose a ~ariety of embo~sing ~heet~ and tape~.
U.S. Patent~ 2,599,359, i~ued June 3, 1952 to American Cyanamld Company7 3,073,734, i~ued January 15, 1963 to ~ohn~on &
John~on7 3,447,997, ia~ued June 3, 1969 to Formica Corporations 3,562,088, i~sued February 9, 1971 to The Xendall Company; 3,600,268, iJ~u-d Augu~t 17, 1971 to Nilto Electric Industrial Co. and 3,623,944 i~ued November 30, 1971 to Compac Corporation disclo~o a variety of film laminates having a variety of function~, particularly 8 adhe~ive tape~
SUMMARY OF TH~ INVBNTION
Novel embo~able plastic a~emblies are provided having a thin film of a tre~s whitening, ~ubstantially tran~parent and haze fr-e ~la~tomer-modifiod poly(methyl methacrylate) adhered to a non-atrea~ whitening, opaque polymeric bacXing. Either the backing i~
colored, or a pigmented film i~ introduced behind the backing away from the ~tre~ whitening film. Normally, an adhe~ive coating i8 then applied to the backing and protected by a releasable liner.
The resulting film provides sharply defined alpha-numeric ~ymbols, sub~tantially free or free o~ gho~ting, without rupture upon embo~ing. Furthermore, the film i~ stable for long periods of time without substantial 1088 of the stre~s whitening, despite normal variations in temperature.
BRB F DESCRIPTIO~ OF THB DRAWI~GS
Fig. 1 i~ an enlarged side elevational view, in ~ection, through an embo~sed section an a tape constructed in accordance with the pre~ent invention;
Fig. 2 i~ a plan view of a letter embo~ed into a tape constructed in accordance with the pro~ent invention;

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~04~i183 Fig~. 3 and 4 are similar to Figs. 1 and 2, but illu~trate the con~truction of prior art tapes and the appearance of a letter, togethe~r with a ghost image, embo~ed onto a prior art tape; and, F$g. 5 i~ an enlarged ~ide elovat~onal view, in section, through a composite multilayered tape con~tructed in accordance with the pre~ent invention.
DESCRIPTION OF THE SPECIPIC EMEODIMENTS
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The composite assembly of thi~ invention comprise~ a Jtre~
whitening film, optionally a pigmented layer, if the backing i9 clear or white, a backing layer, preferably pig~ented, an adhesive coating and a protective ~trip. The assembly can be in large ~heets, tapes of from about 1/4~ to 3/4" in width, and the like. The assembly can vary widely in thickne~ generally being at lea~t about 8 mil~ in thickne~ and u~ually not exceedlng 50 mll~ in thickne~s, more u~ually being in the range of about 8 to 20 mil~ in thicknesa. The particular thickne~ a function of the ombos~ing die with which the tape or 4ilm is to be usQd.
The base or ~tress whitening sheet will normally be of from about 2 to 6 mil~ in thickness, more u~ually in the range of about 3 to 4 mils in thickness~ The ten~ile elongation of the film material when te~ted in accordance with ASTM D-638 (0.25 in. ~pecimen 0.2 inches per minute) will have an elongation at brea~ of at least about 25%, more u~ually at least about 40% and generally not exceed-ing about 80X, more usually not exce-ding about 70X. The Izod Impact Strength (ASTM D-256) notched for a 1/8" specimen at 25C
will usually be in excess of 1.0 ft.lb~inch of notch, usually in excess of 1.5 and u~ually not exceeding about 2.1. ~aze (ASTM D-1003) will generally bc le~s than lOX for a 0.125" thick speci~en.
The polymer has a major amount of a methyl methacrylate lV46183 Lymer and a minor but ~ufficlent amount of an ela~tomeric inter-polymer, u~ually at lea~t 10 weight percent, and genorally not exceeding 40 weight percent of the total compo~ition, u~ually from 15 to 35 weight porcent of tho total composit~on.
The methyl methacrylate polymer m~y have from about 0 to 20 monomer porcent of anoth2r monomer, u~ually an alkyl acrylate wher~in the alkyl group i8 of from 1 to 6 carbon atom~, more usually of from 2 to 5 carbon atom~. The polymers will usually have a visco~ity average molecular woight in the range of about 7S,000 to about 250,000, more u~ually of about 100,000 to 2~0,000. The methyl mothacrylate polymer ~ay be bonded to the ela~tomer modifier or the elastomer difier may bo a mixture with the methyl methacrylate polym0r.
An ela~to~er modifior i~ provided for combination with the mothacrylate polymer. The polymers may be cro~s linked or mechanically mixed. The lastomer modifier i~ convoniently an acrylate polymor having one or more of other monomer~. Usually, the acrylato will be pre~ent in at lea~t about S0 monomer percent and normally not ~xceeding about 70 monom~r percent. The acrylate i~
an alkyl acrylate of from 1 to 6 carbon atoms, more u~ually of fro~
1 to 4 carbon ato~a. Small ~ount~, generally from about 0.1 to 2 m~nomer percent are added of cro~s linking ~onomers that i~, ~ono~er~
which have two actiYe non-conjugated ~with each other) d~uble bonds.
Il~u~trative cro~J linking monomer~ include alkylene diacrylates, alkyl methacrylate, and the like. The remainder of the monomer~ will be derived ~rom aromatic addition monomors, ~uch a~ ~tyrene, alkyl methacrylate~ ~alkyl of from 1 to 4 carbon atom~) and hydrophilic addition monomer~, such a~ hydroxyalkyl, alkoxyalkyl, or alkylthio-oxyal~yl (alkyl of from 2 to 4 carbon atom~) acrylates and methacryl-lV~6183 es~ vinyl pyrxolidone, acrylonitrile, and the like. Of particular interest are the hydroxyalkyl methacrylate~ and acrylates. The individual monomers will normally be present in from 0.1 to 15 monomer percent with styrene present in from about 5 to 15 monomer percent and the other monomers in from about O.l to 5 monomer percent.
The above polyme~s are illustrated in French Patent No.71/07305, filed December 27, 1971. Elastomer modified methacry-lates are commercially available from Rohm and Hass co.~ west Philadelphia, PennsylvaniaJ under the trade mark P~E~IGL~S DR, specifically DR-42 and from American Cyanamid Co., ~ew YorkJ
~ew York, under the trade mark XT POL~MER, specifically XT-375.
In accordance with th~ invention, the base film is normally and preferably adhered to a rigid plastic backing. ;
Conveniently, the plastic backing can be any of a wide variety of suitable plastics to which the methacrylate polymer readily adheres, which are reasonably stable to light and heat, have a similar coefficient of expansion to the methacrylake polymer, and provide the desired degree of mechanical strength, while still being embossable, so as to retain the desired structure after being embossed with a die. Among the various polymers which may be used are such addition polymers as polyvinyl chloride, copolymers of vinyl chloride and vinylidene chloride, copolymers of vinyl chloride and vinyl acetate, polypropylene, and the like. The backing will commonly be of a thickness of about 2 to 6 mils, usually 2 to 4 mils.
If desixed, a colored coating may be introduced behind the backing whe~e the backing is transparent. The coating will vary from a fraction of a mil to 1 mil in thickness and can be applied according to conventional means, such as spraying, .
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1~)4~;183 :ushing or the like, The coating provides a colored background which i8 aesthetically pleasing, and enhances the legibility and clarity of the embossed symbol. Conveniently, a paint binder such as Union Carbide's VYHH may be employed. Preferably, and a~ternativsly, the backing is colored with one of a wide variety of dyes and pigments, particularly those providing red, brown, green or blue coloration. The dye may be a soluble~or insoluble dye as described in aforesaid U.S. Patent No.2,925,625, column 4.
The base and backing may be joined together by having the two compositions coextruded as sheets and calendared, by laminat-ing, or other techniques well known in the art.
In a preferred embodiment, the base and backing are annealed at a temperature at or above 200 F, after the joining of the two films.
To the exposed surface of the backing, an adhesive layer i8 applied by conventional means. Various adhesives may be used, such as those described in aforesaid U.5. Patent No.

2,953,475 and aforesaid U.S. Patent No. 3,036,945. See particu-larly column 3 of the latter.
Finally, a protective layer is placed over the adhesivelayer. The protective layer may be any of a wide variety of easily removable films, such as a metal film, e.g. aluminum, a plastic film, e.g. polyethylene, fabric, e.g. cellulosic, or the like. The thickness of the protective layer will be at least about 2 mils, generally not exceeding about 10 mils, and usually in the range of abou~ 4 to 8 mils.
Turning now to consideration of the drawings. Referring to Figs. 1, 2 and 5, embossing tape 2 constructed in accordance with 104~83 a pre~ent invention compri~e~ a clear tran~parent or translucent ~ethacrylate base 4, backing 6 adherod or affixed to the base, an adhe~ive coating 8 and a protective ~rip 10, that can be peeled off the adhe~ive to expo~e the latter for adhering the tape to a support ~urfac~, (For the purpo~e of thi~ ~pecificatlon and tho clai~, the term~ "clear", "tran~parent" and "tran~lucent~ are used inter-changeably, and the term ~transparent" i~ intended to include the other~). The ba~e 4 is constructed of an ela~tomer modified meth-acrylate. BacXing 6 i~ a non-~tre~s whitening rigid plastic, which 0 i8 pigmented unless a colored coating iB provided at the back of the bacXing. The base and backing are affixed to each other by a bonding agent, heat sealing, coextrusion, and the like.
The adhe~ive layer 8 i~ coated onto the exposed backing and prot-cted by protective ~trip 10.
The tape is provided of a thicknes~ and width in rolation to the embo~sing machine to which it is intended. It enters the embo~sing machine longitudinally and lotters, ~ymbol~ and the like are sequentially embos~ed on the tape at spaced intervals. By deform-ing the tape, by raising tape portion~ or sections 12 above the flat remainder of the tape, as illustrated in Fig. 1, the raised section i9 stressed beyond the yield point of the stres~ whitening methyl methacrylate film. A stre~s whitened area 16 extend~ a relatively short distance to either side of an imaginary central line of raised ~ection 12, that terminates wel} short of the flat tape remainder 14.
Maximum stresses in the base appear in the vicinity of its convex exterior curvature 18. Substantially no stress whitening is experienced in the area of ~he concave exterior surfaces 20 of the base. This lesser stressed area can result in stress whitening, creating a ghosting or halo effect, in embos~ing tapes which do nDt llow the t-aching of this invention. In the ~ubject embosRing tape, the ~tross whiten~d area i~ limited to the im~ediate vicinity of the imaginary center of raised ~ection 12, thu~ leading to a ~harply dofined, ~tres~ whitened symbol, ~uch a~ the lotter ~"
illu~trated in Fig. 2.
As an alternative to pigmenting the backing a coating of an ink or paint 22 may be placed away from the base 4 on the backing 6. A letter embos~ed on the tape 2 has a background, color and appearance supplied by the paint 22 and stress whitening solely from the baqe 4.
Referring briefly to Figs. 3 and 4, for purposes of illu~tration, there is shown an embossing tape constructed in accordance with the prior art. Such prior art tape comprises a layer 24 of the ~tre~o whitening material such a~ polyvinyl chloride, a ~uitable adhes~ve and a protective ~trip (not ~hown in the draw-ing~). Upon emboJ~ing of this prior art tape, a stress whitened area 26 i~ formed which extends from an imaginary center line of ths rai~ed section to a flat remainder 28 of the tape. As compared to the tape of the present invention, the stress whitened area extends substantially further away from the imaginary center line.
In the transitional area 30, between concave and convex tape portions 32 and 34 respectively, only limited stress whitening takes place, leaving dark areas 30. The stress whitening which occurs at the concave portion 32 creates an unsightly and undesirable ghost or halo 36. Con~equently, a letter, such as letter l'LU as ~hown in Fig. 4, embossed on prior art tape, has a peripheral ~econdary or ghost image 36, which di~trac~ from its appearance.
In a letter embossed on tape constructed in accordance with the subject invention, such ghost iMages do not form, because 1~)4~183 8 ~tres~ whitened area 16 terminates at about the transition between the convex and concave surface portions of the raised ~ection and because the lower portion of the tape (which i8 the portion that stre~ whit-n~ the furthest away from the center line in the prior art tape) doe~ not ~tre~s whiten at all.
Although normally the ba~e 4 i~ tran~parent, ~o that the colored backing can be viewed through the base and provide the desired background color of the tape, in some situations it may be de~irable to color the ba~e 4. Any coloring should be consi~tent with the coloring of the backing, and ~hould not be detrimental to the stres~ whitening characteristic of the ba~e.
In accordance with the subject invention, larger letter~
can be achieved with greater ~troke width, without letter fracture, and clarity and legibility is enhanced by the ab~ence of gho~ting.
The white resulting is a sharper, clearer white than previously attained with earlier tapeJ.
The following examples are offered by way of illustration and not by way of limitation.
Example I
An 0.004 inch thick base was constructed from Rohm and A Haas DR-42 elastomer-modified-poly(methyl methacrylate). An 0.002 inch layer of a pigmented, non-stress whitening rigid vinyl (PVC) backing was af~ixed to the base. The backing was adhesive coated and the adhesive was protected by an 0.006 inch polyethylene relea~e liner.
The thus constructed tapo, when embossed, showed sharp embossing outline~ free of ghost images.
Example II
A backing constructed of an 0.004 inch non-stress whiten-104~183rigid vinyl wa~ affixed to the same ba~e a~ the one used in ~xample I. The resulting tape showed clear, ~harply defined ombo~lngs free of gho~t image~.
~xampl~
~-~ An 0.004 inch thick backing of pigmented Mar~on'~ Cycolac CG-AES compound wa~ affixod to the ~ame bas- a~ was u~ed in Exa~ple 1. A~ in Example I, embossings on th tape were clear, ~harply defined and free of ghost images.
~xample IV
An 0.004 inch thick backing constructed of pigmented Dow Chemical Styron 470 high impact poly~tyrene re~in wa~ affixed to the same base a~ wa~ used in Example I. Embossings on the tape were again clear, sharply defined and without gho~t imag-~.
Example V
A baJo ~onJtructed of an 0.004 inch thick W-8tabilized American Cyanamid XT-375 elaJtomer modified poly(methyl methacrylate) was affixed to an 0.002 inch thick pig~ented layer of rigid vinyl which, in turn, received an adhesive coat and a polyethylene release liner. ~mbossings on this tape were again clear, sharply defined, ad without ghost images.
~xample VI
The American Cyanamid XT-375 base wa~ combined with the same backings a~ was the Rohm and ~aa~ DR-42 liner. In addition, both the Rohm and ~aas DR-42 and the k~erican Cyanamid XT-375 base~
were oombined with the variou~ liners listed in Examples l-IV but a coat of paint was applied to the ~ide of the backing attached to the ba~e and no pig~entation wa~ used in the backing. In all in~tances, the embG~sing~ on the tape were clear, sharply defined and fre~ of ghost images.

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104~183 In accordance with thi~ invention, novel embo~Jing tapo~
are provided which provids excellent ~tability for long periods of time to temperaturo~ and light which are encounterod in storage and uae. When exposed to weathering under ~evere condition~, the tape w~ found to retain the de~irable emboJ~ing characteri~tic~ far long period~ of time. The e~bossing tape~ provide clear, Jharply dofined character~ undi~torted by gho~ting and without lett-r fracture.
In addition, the stress whitening obtained i8 very opague and bright, ~o a~ to provide enhanced clarity and legibility, further enhancing the deoired characteri~ticJ of the embos~ing tape.
~ lthough tho foregoing invention ha~ been de~cribed in aome detail by way of illustration and exa~ple for purpo~e~ of clarity of under~tanding, it will be obviou~ that certain changeo and modificationa may be practiced within the acope of the appended claim~.

Claims (17)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. An embossable sheet material comprising a rigid non-stress whitening plastic backing film and a base sheet of at least 2 mils in thickness of a stress-whitening elastomer modified poly(methyl methacrylate) having a tensile elongation of from 25 to 80 per cent of elongation at break, the elasto-meric modifier being bonded or mixed with poly (methyl methacry-late).

2. An embossable sheet material according to Claim 1, in which the backing film is of a thickness of from 2 to 6 mils.

3. An embossable sheet material according to Claim 2, having an adhesive layer adhered to the exposed surface of the backing film and a protective liner for the adhesive layer.

4. An embossable sheet material according to Claim 2, wherein the base sheet is transparent and the backing film is opaque and pigmented.

5. An embossable sheet material according to Claim 2, having a pigmented coating on the backing film.

6. An embossable sheet material according to Claim 2, wherein the backing film is polyvinyl chloride.

7. An embossable sheet material according to Claim 1, in the form of an embossing tape, for use in machines of the kind for impressing onto the tape alpha numeric symbols, wherein the base sheet is transparent and from 2 to 6 mils in thickness, the backing film is affixed to the base sheet, an adhesive coating is affixed to the exposed side of the backing film and a protective liner is adhered to the adhesive coating.

8. An embossable sheet material according to Claim 7, wherein the elastomer modified poly(methyl methacrylate) contains an acrylate polymer as the elastomer modifier.

9. An embossable sheet material according to Claim 7 or claim 8, wherein the backing film is a polyvinyl chloride.

10. An embossable sheet material according to any one of Claims 7 to 9, wherein the backing film is pigmented and is opaque.

11. An embossable sheet material according to claim 7, wherein the total thickness of the tape is from 8 to 20 mils.

12. An embossable sheet material according to claim 7, having a pigmented coating on the backing film.

13. An embossable sheet material according to Claim 1, in the form of an embossing tape, for use in machines of the kind for impressing onto the tape alpha-numeric symbols, wherein the base sheet is transparent and has an acrylate poly-mer as the elastomer modifier, an adhesive coating is provided on the exposed side of the backing film, and a protective liner is adhered to the adhesive.

14. An embossable sheet material according to Claim 13, having a total thickness of from 8 to 20 mils.

15. An embossable sheet material according to Claim 13, wherein the backing film is formed of polyvinyl chloride.

16. An embossable sheet material according to Claim 13, wherein the backing film is formed of polypropylene.

17. An embossable sheet material according to Claim 13, wherein the acrylate polymer is cross linked to the poly(methyl methacrylate).