CA1187259A - Method of obtaining special effects in mortar areas of embossed foamed plastic sheets - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

Method for producing a dull, a grainy, or a sparkling surface on the depressed (mortar) areas of a chemically em-bossed foamed organic plastic sheet. The sheet is prepared conventionally except that a tacky coating is formed in the mortar areas while maintaining a state of dryness in the land areas; especially by use of a radiation-curable poly-urethane coating which is cured in the land areas by radia-tion while the mortar areas are masked. Inert particles or flakes distributed over the tacky mortar areas create the desired surface effects when the polyurethane composition in these areas is cured; which is preferably done by the heating employed in the conventional foaming operation.

Description

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¦ METHOD OF OBTAINING SPECIAL EFFECTS IN MORTAR AREAS
OF EMB~SSED FOAMED PLASTIC SHEETS

Back~round of the Invention ;

This invention relates to production of chemically embossed foamed organic plas~ic sheets having special effects such as a dull, a grainy, or a sparkling surface in the so-called moFtar areas (depressed areas~.

The art of producing chemically embossed foamed organic plas~ic sheets useful for floor covering, wall covering, table covering, and the like is well-known, as represented for example by United States Patent 3,~93,094 of December 20, 1966, to Nairn et al for "Textured Foam Processes". In general, such processes involve steps of:
(1) Forming a sheet of organic foamable thermo-plastic, especially PVC resin ~polyvinyl chloride) in the form of a plastisol or organosol upon a substrate such as an asbestos mat, or a cellulosic felt sheet, or release paper, or a PVC sheet~ The foa~able plastisols conventionally contain besides PVC ~dispersion grade) and plastici7er, one or more stabilizers for PVC (heat and light stablilizers);
and contain a blowing agent decomposable by heat to generate gas which causes ~he hea~ed resin compos ition ~o foam. One or more cat~lysts of decomposi-tion of the blowing agent can be includ~d to reduce the exposure to heat which will be needed to cause ?5 foaming~

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t2) ~ellin~ the plasLisol ~r or~ano~ol by I~C~L
to the point that its sur~ace can be printed upon, e.g. by screen printing, gravure printing, or transfer printing; but maintaining the exposure to heat short of that which causes substantial foaming of the plastisol.

(3) Printing upon the gelled surface, e.g. by screen printing, gravure printing, transfer printing, or other methods of printing, usin~ a composition formulated like a printing ink and consisting essentially of a foaming inhibitor, i.e.~ an inhibitor for the decom-position of the blowing agent, which inhibitor generally will be dissolved or dispersed in a liquid carrier.
, This inhibitor composition, hereinafter sometimes re-ferred to as "ink", can contain one or more pigments, a carrier for the pigment such as a vinyl resin, and a plastici~er for this carrier resin to improve its adhesion to the gelled PVC surface. Numerous com-pounds have been identified as inhibitors of decom-position for use with various blowing agents. The above cited Nairn et al patent designates eleven classes of such inhibitors and lists specific examples of each class~

(4) Coating the sheet, after printing, with a layer of organic plastic serving to improve the wearing properties of the shee~. The same resin as used in the foamable plastisol can be used for this wear layer; or a different resin can be used, especially as an additional top coat. Specifically, radiation-eurable compositions of urethane oligomers, together with acrylate monomers containing at least one acrylyl 1~ ~37~

group (or methacrylate monomers or others) and a photoinitiator have been recommended for use as a wear layer over an expanded vinyl foam and a clear vinyl overlay. See U.S. Patent 4,100,318 of July 11, 1978 to McCann et al for "Actinic Radiation Cured Coatin~ for Cushioned Sheet Goods and Method": Abstracti col. 11, line 32 - col. 14, line 2: Example II at col. 14; col. 18, line 67 -col~20, line 32.

(5~ Heating the sheet to cause foaming and to raise the land areas by the resulting expansion in the land areas and to fuse the thermoplastic com-ponentsof the sheet, while leaving the mortar areas flat or substantially so, as a result of 1~ presence therein of foaming inhibitor contacting and diffusing into the foamable composition. This heating step can precede a step of curing a rinal top coat as in the above U.S. Patent 4,100,318.

Summary of the Invention In accordance with this invention, a chemically embossed f~amed sheet of organic plastic is produced ha~ing raised surface areas or lands and depressed surface areas or ~ortars generally as in the prior art, but on ~he areas designed to be mortars a coat-ing containing a tacky organic resin polymerizable to a dry cured state is formed, while maintaining or developing or in general establishing a dry state in land areas~ Then particles or flakes of inert solids which adhere to the tacky resin are distributed over the mortar areas, and are dusted off the dry areas of the sheet, e.g. by blowing off, brushing off, wiping ~ ~7~

off or the like. ThereaEter the tacky resin is cured to dryness, preferably by the heating employed in the foaming step.

The lesulting product is an embQssed foamed sheet having in the mortar areas, special e~Eects imparted by the inert solid incorporated therein, such as a dull, a grainy, or a sparklin~ eE~ect.

I`he invention is not susceptible of illustration by a drawing~

D iled Description The preferred method in accordance with this invention for forming a coating of tacky organic resin upon the top surface of areas of the organic plastic sheet, designed to be mortars, is to apply over the whole top surace o the sheet a composition con-~0 sisting essentially of crosslinkable polyurethane oli-gomers and a crosslinking agent therefor, and to main-tain this composition in a tacky state in the areas designed to be mortars while curing the composition to dryness in the areas designed to be lands.

Various e~pedients such as applying poly-merization inhibitors to the mortar areas can be adopted to obtain the desired diferential curing of the poly-urethane composition. The best mode contemplated by t~e inventor, ho~Yever, is to employ a polyurethane composition curable by radiant energy (actinic radiation or ionizing radiation~, and to mask fxom the radiation, the mortar areas of the sheet. Choiee of the masking material will depend somewhat on the specific radiation being used~ Suitable choices will be obvious to those skilled in the art of polymerization by use of radiant energy and the present invention does not reside in such choices.

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Polyurethan~ c~mp(~itions ~uri~b1e by radiant eller~y, ~ sui~ble f~r us~ wear layer on rvc foameu resiil sheets, are known per se for example, as disclosed in the above cited U.S. Patent 4,100,318. Preferred com-positions for use in the method ~f this invention employ-ing ultraviolet radiation for curing in the land areas, comprise polyurethane oligomers terminated by acrylate or methacrylate groups, such as the acrylourethane oligo-mers disclosed in the above cited U.S. Patent 4,100,318 at col. 18, line 62-col. 19, line 18; toge~her with a crosslinking agent such as pentaerythritol triacrylate or trimethylolpropane triacrylate and an aromatic car-bonyl compound photoini~iator such as benzoin butyl ether.

Such compositions, as previously s~ated, are applied 1~ over the whole top sùrface of the PVC sheet, either before or after the sheet is heated for foaming.

If before, then a mask is positioned over the sheet to shield the intended mortar areas from radiation; radi-ant energy, especially ultraviolet radiation, is directed ~0 through the mask onto the land areas to cure them to dry-ness while maintaining the polyurethane composition in the mortar areas in tacky condition; the inert solid particles or flakes are distributed onto the sheet, particularly to the mortar are~s where they adhere to the tacky poly-'5 urethane co~position; and the excess solid is dusted off the dry areas. T~en ehe sheet is heated eo expand the foamable plastic in the land areas while leaving the mor-tar areas substantially ~lat and to fuse the PVC resin.
The crosslinkable polyurethane composition in the mortar ~0 areas is cured by heat, during this foaming step, to fix the iner~ solids in place; or can be cured ther~after by heat or by exposure to radiation.

I~ the foamable PVC sheet is foamed before the cross~
linkable polyurethane composition is applied thereLo, the above procedure involving exposing the polyurethane composition to radiation through a mask i5 again employed as before, followed as before by distributing particles _. ~

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or flakes of inert s~lids onto the sheet and dusting off the excess from the dry areas. The desired registry of the mask with the mortar areas may be easier with the lands already formed. The tacky polyurethane composition in the mortar areas between the lands is cured by hea~ing or by radia~ion to fix th~t inert solids in place.

The inert solids distributed upon the mortar areas and adherent to the polyurethane composi~ion which is maintained in tacky state in the mortar areas until the inert solid has been distributed thereon, can be any one or more of various pigments, fillers, powders, parti-cles, flakes and the liket the only requirements are that they be stable under the exposure involved to radi-ation and/or heat, have no adverse effect on the other ingredients there present and be adherent to ~he tacky areas. These are not demanding requirements; and in practice, many desired pigments, fillers, particulate matters, or flaXes can be used including inorganic and organic pigments, such as phthalocyanine pigments, ti~
tanium dioxide, carbon black, silica; and chrome, cobalt and copper pigments; particulate matter such as fine and coarse sand; flakes such as mica and aluminum metal, and many others. The particle diameter of these inert so-lids can lie an~here in a wide range, say from that of very fine pigments (about ~.01 micron) up to that of very coarse sand (about ~ millimeters)~ Such inert solids in the mortar areas impart a dull, a grainy, or a sparkl-ing surface to the mortar areas.

One alternative to the fore~oin~ procedure ~involv-ing coating the top surface of the sheet with a radia-tion-curable composition and masking off the mortar areas during irradiation of the coating,) is as follows. Only the areas of the sheet designed to be mortar areas are coated, before foaming of the sheet, with a cros~linkable polyurethane composition as previously described and con-I 1."~ ~
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taining a freL r.(dic~l polyn~eri,:;ltion ~-alyst or initi-ator. This composition preferably is an ln~redient of the ink coating which contains also a foaming inhibitor and which is printed onto the gelled surface of the PVC sheet.
The crosslinkable polyurethane composition can be ~acky or liquid, so long as the ink coatin~ on the mortar areas is made tacky.

The ink coating composition, as is known, must be sufficiently compatible with the foamable gelled PVC com-position so that the foaming inhibitor included with the ink composition will migrate into the gelled foamable sheet t~ suppress foaming thereof in the mortar areas.

Particles or flakes of inert solids are distributed , as previously described over the mortar areas and dusted off the dry areas, and the sheet is foamed as previously described.

Such free radical polymerization catalyst used along with the crosslinkable polyurethane on the intended mor-tar areas desirably is selected with reference to tPmper-2D ature and time of the foaming operation, whereby to cure the polyurethane during the foaming operation. The cur-ing action of the catalyst can be adjusted by varying the catalyst and/or varying its concentration. Suitable catalys~s include diaryl peroxides such as dicumyl perox-ide. Such polymerization catalysts for promoting the curing of compounds containing unsaturated groups, such as acrylyl groups, are known as indicated for example in Smith et al, ~S. Patent 3,935,330 o January 27, 1976 or "Two-Step Coating Process'`, at col. 9, lines 33-51.

3C~ I desired, a top coat o, î ~r example, a crosslinka~le p~lyurethane can be applied over the whole surface of this sheet after foaming, and then cured by exposure to actinic . . --¢1 -radiation or to radiation creating a heating effect, such as infrared or microwave radiation.

It will be appreciated that use of a proper:ly selected Eree radical polymerizatio-l catalyst as above described, in a coating comprised o:E a cross-linkable polyurethane composition applied over the wilole surEace o:E a Eoamab.l.e thermoplastic sheet and e~posed - prior to foaming - to radiation through a :mask as previously described, will facilitate the desired curing of the polyurethane composition in the mortar areas by -the effect of the heat applied for the foaming operation. By using such a procedure, exposure of the sheet to radiation to cure the poly-urethane composition in the mortar areas will be unnecessary.

The following Example is illustrative of the bes-t mode contemplated by me for carrying out my invention.

1. In the conventional manner for production of chemieally embossed PVC sheet, lay down a foamable PVC plastisol composition, h~at to gel the composition, print with ink containin~ foam inhibitor, and coat with a clear vinyl overlay, which is then gelled.

2. Coat the resultin~ sheet with a com-position containing polyurethane oligomers terminated by aerylate groups (60 parts);
2-ethylhe~yl aerylate (30 parts~; trimethyl-olpropane triacrylate (4 parts); dicumyl peroxide ~10 parts of a commereially available 40~ solution); and benzoin butyl ether (1 part).

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3. Mask the coated sheet to prevent radiation from reaching the areas printed with the ink containing foam inhibitor, and e~pose to ultraviolet radiation from a medium pressure mercury vapor arc, in a nitro~en atmosphere, for a few seconds to cure the crosslinkable polyurethane composition in the intended land areas to dryness while maintaining the mortar areas in a tacky state.

4. Discontinue the radiation; remove the mask and distribute over the mortar areas whatever inert solids are desired to obtain a dull, grainy or sparkling surface, such as a silica pigment, carbon black, or aluminum flakes as used in aluminum pain-ts, or a mi~ture thereof.

5. Dust off the e~cess solids from the dry areas of the sheet, suitably by blowing off with a pufE of nitrogen.

6. Heat the resulting sheet in a nitro~en atmosphere to fuse the PVC resins and bond them to the polyurethane coat, and to foam the sheet and cure the polyurethane com-position in the mortar areas.

7. Cool the resultin~ sheet.

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Claims (8)

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

1. In a method of producing a chemically embossed foamed sheet of organic plastic, having raised surface areas or lands and depressed surface areas or mortars, the improvements for imparting special effects to the mortar areas, comprising:
(i) forming a tacky coating upon the top surface areas of a foamable polyvinyl chloride resin sheet, designed to be mortars, of a composition containing a foaming inhibitor and thereafter a composition consisting essentially of crosslinkable polyurethane oligomers and a crosslinking agent therefor, while maintaining or developing a dry state in the land areas, charact-erized in that:
(a) the polyurethane composition is maitained in tacky state, only in areas or said sheet designed to be mortars; and (b) inert particles or flakes adherent to the tacky areas, having average particle diameter in the range from about 0.01 micron to about 2 millimeters, are distributed before or after step (ii) over the tacky areas and are then dusted off from areas which are dry; and curing the tacky areas to fix the inert solids in place; and (ii) heating said sheet to cause foaming only in the land areas, and to fuse the thermoplastic components of the sheet.

2. Method of claim 1, wherein the crosslinkable polyurethane composition is curable by radiation and is cured to dryness in the land areas, while remaining tacky in the mortar areas, by exposing the polyvinyl chloride sheet, coated with radiation-curable polyurethane composi-tion, to radiation which causes the polyurethane composition to cure; using a mask which admits the radiation to the land areas while at least reducing the intensity thereof over the mortar areas.

3. Method of claim 2, wherein the radiation employed is ultraviolet radiation.

4. Method of claim 3, wherein the whole top surface of the foamable sheet is coated with a composition containing both a crosslinkable polyurethane composition and a catalyst of thermal polymerization at concentration causing the polyurethane composition to cure under the influence of the heat used to cause foaming and expansion in the land areas; and the exposure to radiation through the mask is carried out prior to foaming of the foamable sheet.

5. Method of claim 2, wherein said polyurethane is terminated by acrylate or methacrylate end groups;
said crosslinking agent is at least one compound selected from pentaerythritol triacrylate and trimethylolpropane triacrylate; and an aromatic carbonyl compound photo-initiator is contained in the crosslinkable coating composition.

6. Method of claim 5, wherein the heat applied to the sheet for purposes of foaming and fusing the polyvinyl chloride resin simultaneously cures the poly-urethane composition in the mortar areas.

7. Method of claim 5, wherein the tacky polyurethane composition remaining in the mortar areas, after curing of the coated land areas and expansion there-of by foaming, is cured by exposure to radiation.
8. Method of claim 1, wherein the cross-linkable polyurethane composition is curable by heat and

Claim 8 cont'd...

contains a catalyst of thermal polymerization, characterized in that the said polyurethane composition is applied only to the areas designed to be mortars and is maintained in a tacky state, until the inert solids have been distributed thereover; and thereafter is cured by heat to fix the inert solids in place.