GB2347881A - Process for manufacturing a surface covering - Google Patents

Abstract

A vinyl film is provided with an electron beam cured wearlayer. The preferred coated printed film is prepared by applying a polyester urethane acrylate composition to a printed sheet of rigid vinyl film and exposing the coating to a low energy electron-beam, forming an abrasion-resistant topcoat with no substantial degradation of the printed rigid vinyl film. The electron beam radiation has an energy level less than 135 KeV.

Description

SURFACE COVERING AND PROCESS FOR ITS MANUFACTURE This invention relates to a surface covering, advantageously to a floor covering product, in which a wearlayer composition, preferably an acrylated urethane composition, is coated onto an underlying layer, especially a layer in film form, and more especially a polyvinyl chloride (PVC) or vinyl composition film, preferably a rigid vinyl film, to form a composite. In one embodiment, the composite is laminated to a surface covering substrate and embossed. If the product is a floor covering product it may be a floor tile or a floor covering sheet. The invention also relates to a process for the manufacture of the surface covering; in a preferred process, the composite is laminated to the substrate on a belt or drum line to form the final product.

It is common in the manufacture of a surface covering to include as a final or external layer of a multi-layer covering a, usually transparent, layer, which because its primary function is to protect the underlying layer, which is usually a decorative layer, is termed a wearlayer. The wearlayer is desirably cured, or crosslinked. It has been considered to use ultraviolet radiation to effect curing; this has, however, not proved satisfactory for the following reasons: Commercially available medium pressure ultraviolet mercury lamp sources have a strong infra-red component which results in excessive heating of the coating composition and the film. The infra-red component may be as much as 60% of the total lamp power. Curing the wearlayer material on rigid vinyl film by a W lamp results in film distortion as a result of the film's exceeding its glass transition temperature.

Distorted film cannot be processed into a commercially acceptable floor tile. Further, when the film is laminated, the coated side tends to adhere to the laminator rather than release from the laminator roll, because the coated side is only partially cured.

The present invention provides a surface covering comprising a wearlayer/film composite, the wearlayer comprising a composition including a cross-linked organic moiety, the film comprising a vinyl composition, the film having a thickness of no greater than about 0.5 mm, the wearlayer composition having been cured with electron beam radiation, and the film having a product Delta b of no greater than 2 as measured by the difference between the +b (yellow) value of the wearlayer/film composite on a calibration plate and the +b (yellow) value of the calibration plate alone.

Further, the invention provides a surface covering comprising a wearlayer/film composite, the wearlayer comprising a composition including a cross-linked organic moiety, the film comprising a vinyl composition, the film having a thickness of no greater than about 0.5 mm, the wearlayer composition having been cured with electron beam radiation, and the film having a Delta b of no greater than 2 as measured before coating of the wearlayer composition and after curing of the wearlayer composition.

The invention further provides a process of making a surface covering comprising the steps of: a. providing a sheet of vinyl film material, b. coating the sheet with a wearlayer composition comprising a cross-linkable organic moiety, and c. curing the wearlayer composition with electron beam radiation, the electron beam radiation having an energy level of less than 135 KeV with a 7.0 cm average gap, and preferably at least 100 KeV with a 7.0 cm average gap.

At an average gap between the window and the substrate of 7.0 cm, a typical electron beam unit will lose approximately 10 KeV per 2.54 cm gap of accelerating energy in a typical nitrogen atmosphere. Hence the effect of an electron beam machine operating at 125 KeV with a gap of 7.0 cm will be similar to that of another similar machine operating at 105 to 110 KeV with a gap of 2.54 cm. Those skilled in the art will be able to determine, either by calculation or routine experiment, the appropriate conditions for the effect in a machine having different characteristics to be equivalent.

To minimize yellowing of the vinyl film, the energy level of the EB radiation is advantageously less than 135 KeV with a 7.0 cm average gap. Preferably, the energy level of the EB radiation is at most 130 KeV with a 7.0 cm average gap. The preferred dosage to cure the wearlayer composition is about 2 to about 4 Mrad.

In a preferred embodiment, the wear layer composition is formed by reaction of a hydroxy-terminated polyester with an isocyanurate in the presence of a multifunctional acrylate. The wear layer composition is cured by the low energy electron beam radiation. The coated decorative rigid film is advantageosly laminated to a tile base and then cut to form the floor tile product.

The present invention is based on a method of making a surface covering having a PVC film which is precoated with a wearlayer, the wearlayer being cured with low energy electron beam radiation. In the preferred embodiment, the acrylated urethane coated rigid vinyl film is cured with electron beam radiation of less than 135 KeV. The low energy radiation does not yellow the decorative PVC film by the degradation processes commonly observed when a polyvinyl chloride film is subjected to EB radiation. The resulting composite structure is advantageously then laminated to a continuous sheet of floor covering base under process conditions that yield an aesthetically acceptable composite and then the sheet is cut into floor tile.

"Rigid vinyl film"is a term of art which means a polyvinyl chloride film having fewer than 5 parts plasticizer per hundred parts by weight of resin (phr).

Preferably, there is substantially no added plasticizer in the rigid vinyl film.

The accompanying drawings illustrate various embodiments of the invention.

Figure 1 is a cross-section of one form of wearlayer/film composite of the present invention.

Figure 2 is a cross-section of one form of laminated surface covering of the present invention.

Figure 3 is a schematic representation of a process for making a wearlayer/film composite of the present invention.

Figure 4 is a schematic representation of a process to laminate and emboss wearlayer/film composite of the present invention to a substrate.

Figure 5 is a schematic representation of a second process to laminate and emboss a wearlayer/film composite of the present invention to a substrate.

Referring to Figure 1, a wearlayer/film composite of the present invention has a polyvinyl chloride film base 1. In the preferred embodiment, the base is a rigid vinyl film which is printed on one side with an ink layer 2. The wearlayer 3 is a cross-linkable organic containing composition which is cured in contact with the printed film with a low energy electron beam radiation.

The wearlayer composition includes an organic moiety which is cross-linked by the EB radiation. The preferred organic moieties are ethylenic, acrylic and epoxide.

Epoxide moieties have been cured by EB as described by P. A. F. Buijsen in a dissertation entitled"Electron Beam Induced Cationic Polymerization with Onium Salts." The wearlayer is preferably about 25 to about 76 microns in thickness. As shown in Figure 2, the wearlayer/film composite is laminated to a surface covering base 4 to form the preferred surface covering of the present invention.

Referring to Figure 3, the polyvinyl chloride film 1 is fed into a coater 6 such that the side opposite the decorative ink layer 2 is coated with the wearlayer composition. The preferred polyvinyl chloride film is a rigid vinyl film having a thickness of no greater than about 0.5 mm, more preferably no greater than about 0.25 mm, and most preferably about 25 to about 76 microns in thickness.

The method of coating application may be, but is not limited to, a wire wound rod or a three roll coater. In the reverse roll coater shown in Figure 3, the film passes through the nip between the backing roll 7 and applicator roll 8. The metering roll is indicated by reference numeral 9.

The temperature of the rolls is kept well below the glass transition temperature of the film, e. g., 176 F (80 C), but warm enough to maintain the resin viscosity low enough to provide for improved flow characteristics, thereby eliminating coating defects commonly observed with high viscosity coatings.

The coated film enters the nitrogen inerted processing zone 10 of the electron beam unit where energetic electrons initiate radical polymerization of the ethylenic groups of the coating composition. After the wearlayer is cured, the wearlayer/film composite 15 is rolled onto a small diameter windup core 16.

The wearlayer resin composition used in this invention is chosen to exhibit performance properties sought in the surface covering. For floor covering products, the wearlayer properties include good stain resistance and gloss retention as well as sufficient toughness to resist gouging from foot wear traffic. For the purpose of this invention, the floor coverings must also display a certain degree of flexibility. A non-flexible floor covering that exhibits low elongation can result in the formation of across machine direction fractures once the composite film is wound onto the core Although not limited to polyurethane polyester, resin compositions that are useful as the wearlayer composition of this invention include the reaction product of a diisocyanate and/or isocyanurate structure, a polyester polyol and a polyester having hydroxyl and acrylic functionalities, or the reaction product of a hydroxy terminated aromatic polyester formed from the reaction product of polycarboxylic acid (s), excess diol and acrylic acid. Other wearlayer compositions useful in the present invention include (meth) acrylated polyesters in which the polyester is the reaction product of a tricarboxylic acid or anhydride and a diol, a colloidal silica/acrylate and an epoxide/polyol. (In this specification, the term"acrylic"and"acrylate", and related terms, may include methacrylates although methacrylate-based compositions are presently less preferred.) The preferred polyurethane polyester resin materials are mixed with mono-, di-or tri-functional acrylates to form the wearlayer composition. Other additives may include surfactants and W absorbers.

The second step in the current invention after coating the wearlayer composition onto the rigid vinyl film is to cure the coated rigid vinyl film with ionizing radiation in such a fashion as not to degrade or yellow the rigid vinyl film or alter the appearance of the decorative layer. An electron beam radiation process polymerizes the ethylenically unsaturated groups within the wearlayer resin material causing the composition to change from a liquid to a solid.

The preferred embodiment of this invention utilizes ionizing radiation in the form of low energy accelerated electrons. This method, referred to as electron beam (EB) curing, requires that a nitrogen or other inert atmosphere be above the coating to be cured since the presence of oxygen in high concentrations will result in an undesirable tacky surface.

Since heat in the form of infra-red energy is essentially eliminated by using accelerated electrons, the substrate may be kept below its glass transition temperature and remain free of distortion while the wear layer composition is fully cured.

Typically, commercially available self-shielded electron beam units (Energy Science Inc., or RPC Industries) operate to produce an electron accelerating energy between 150,000 to 500,000 electron volts (150 KeV to 500 KeV). In curing applications where the preferred coating weight is 60 grams per meter square, more than 90 percent of the electrons penetrate into the substrate at an electron energy of 150 KeV. Such energy is sufficient to cause degradation of the rigid vinyl film and result in a yellow appearance that alters the decorative appeal.

Utilizing low electron beam accelerating energy of less than 135,000 electron volts, and preferably no greater than about 130,000 electron volts (assuming an average gap of substrate to window of 7.0 cm) has been found to limit electron penetration into the vinyl film and minimize yellowing of the vinyl film. This is particularly important for white decorative rigid vinyl film where even slight yellowing produces an undesirable effect. E-beam radiation having an energy level 100 of KeV is desirable to ensure proper adhesion between the wear layer and the vinyl film.

By using a low energy electron beam, a film which is susceptible to yellowing more than a Delta b of 2 and is coated with a wear layer composition will not be exposed to excessive electron energy, and therefore will not yellow more than a Delta b of 2. Further, even though the film yellowing is slight, the double bond conversion of the wearlayer composition has been found to be greater than 75%, and even greater than 85%.

The degree of yellowing may be measured by use of a colorimeter that measures tristimulus color values of 'a','b', and'L', where the color coordinates are designated as +a (red),-a (green), +b (yellow),-b (blue), +L (white), and-L (black). It is more appropriate to express the degree of yellowing as a curing Delta b or difference in +b (yellow) values between the initial and final values before and after curing.

A product Delta b may be measured by stripping the wearlayer/film composite from any surface covering substrate, removing any ink or other surface material, and determining the difference in +b (yellow) values between the +b value of the wearlayer/film composite on a calibration plate and the +b value of the calibration plate. For a wearlayer/PVC film composite, an effective method to clean the ink and substrate material from the composite is to wipe it, using a small brush, with a 2: 1 volume ratio of isopropyl acetate: tetrahydrofuran, then with an isopropyl acetate solution, and finally with warm water.

If a Minolta CR300 colorimeter and a Minolta Calibration Plate No. 1933014 are used, typical values of +b for a product in accordance with the present invention are 2.90 for the cleaned composite on the calibration plate and 1.90 for the calibration plate alone. The product Delta b is accordingly 1.00.

A Delta b difference (either curing Delta b or product Delta b) greater than 1 can generally be detected by the naked eye. A Delta b difference greater than 2 is objectionable.

The'dose'or amount of ionizing radiation is referred to as a'rad', one rad being equal to 100 ergs of energy absorbed from ionizing radiation per gram of material. More commonly used terminology is a'Megarad' (Mrad) or 106 rad. The dose required to cure the coating will be dependent on the chemistry of the coating and line speed. In the current application, a uniform dose of 2 to 4 Megarad is sufficient to cure the resin material.

The third step in the preferred process is lamination/embossing of the precoated decorative PVC film to a surface covering base. Two preferred methods for forming a floor covering are on a belt or drum line.

Referring to Figure 4 for a belt line, a vinyl mixture sheet 4 is provided on a conveyor 17 at a temperature of 300 F (149 C) to 330 F (166 C). The composition of the vinyl mixture is resin material, plasticizer and filler to afford a floor covering base preferably 1.1 to 2.0 mm in thickness.

The belt 17 is heated to enable for good adherence of the sheet 4 to the belt 17. The vinyl mixture makes contact with at least one nip. Each nip is formed by two vertically displaced horizontal rolls where the bottom roll is referred to as a backing roll and the top roll is referred to as a laminator or embossing roll.

The coated decorative vinyl film 15 is fed into the first nip 18 (space between two vertical rolls 19 and 20) with the exposed side 21 being the side opposite the wearlayer. In the first nip, the precoated film 15 and floor covering base or sheet 4 are laminated. The heat of the base or sheet raises the temperature of the film above the glass transition temperature in the nip where the film and sheet are laminated.

At the glass transition temperature, the PVC film is stress free and can be embossed. The roll 19 can be an embossing roll thereby allowing lamination and embossing to be carried out in one step.

A second nip 22 can be used to provide an embossed effect on the laminated rigid film/base structure. After the second nip, the surface of the rigid film/base is cooled by pouring water onto the film/base to reduce the product temperature to below the glass transition temperature of the rigid film 15. Stresses that developed during processing as a result of heat will be locked in to afford a flat floor covering structure.

Floor tile may be processed on a drum line.

Referring to Figure 5, the vinyl base sheet 4, maintained at a temperature of 300 F (149 C) to 340 F (171 C), is transferred from a conveyor 23 to a drum 24 that is heated to 180 F (82 C) to give good adherence of the vinyl base sheet. The vinyl sheet 4 is fed through the first nip 25 formed by lamination roll 26 and the drum 24. The coated decorative PVC film 15 is fed into the first nip with the exposed side of the film being the side opposite the wearlayer.

In the first nip, the precoated film and base sheet are laminated. Then the coated rigid film/vinyl base mixture is fed through a second nip 27 formed by embossing roll 28 and the drum 24 to give the product an embossed texture. The temperature of the precoated film/vinyl mixture is kept above the glass transition temperature of the film and coating during the embossing process.

The laminated structure is then cooled by pouring water onto the surface with spray heads 29 while the laminated structure is in contact with the drum. The laminated structure is fed into a water bath 30 which brings the temperature of the rigid film/vinyl base below the glass transition temperature of the film.

The following Examples illustrate the invention.

Acid and Hydroxyl Nos. are expressed in terms of mg KOH/g of material.

ACRYLATED POLYESTER 1 A hydroxy-terminated polyester (polyester polyol) was prepared from the following charge in a 12 liter flask: Trimellitic anhydride 2259 g 1,6-Hexanediol 5334 g Phthalic anhydride 1406 g p-Toluenesulfonic acid 1.8 g The flask was equipped with a heating mantle, stirrer, thermometer, temperature controller, gas inlet tube, and an upright condenser. The condenser was steam heated and packed with glass helices and had a thermometer on top.

The still led to a water cooled condenser that drained into a graduated cylinder. Water evolved during the reaction was collected and measured.

The batch was heated to 428 F (220 C) under a trickle of nitrogen gas (about 14 liters per hour) during which time water of esterification was collected. The reaction mixture was further heated for 5 hours at a nitrogen flow of about 28 liters per hour.

The reaction mixture was cooled and the total amount of water collected was 643 grams. The final product, Polyester 1, had an acid no. of 2.5 and a hydroxyl no. of 207. It therefore had a hydroxy equivalent weight of 274, and an estimated number average molecular weight of 880.

Polyester 1 was acrylated as follows. The materials listed below were introduced into a 2000 ml flask equipped with a mantle, stirrer, thermometer, gas inlet tube, dropping funnel, and Barrett Trap with a water cooled condenser on top.

Heptane 100 ml Polyester 1 800 ml Acrylic acid 277 g Monomethyl ether of hydroquinone 0.1 g p-Toluenesulfonic acid 5.38 g Phosphorous acid 0.6 g Hydroquinone 0.1 g 2,6-Di-tert-butyl-4-methylphenol 0.1 g The trap was filled to the overflow with heptane.

With dry air flow of about 5 liters per hour, the ingredients were heated to reflux at 210 F (98 C) to 221 F (105 C) while stirring vigorously and collecting water and displacing heptane in the trap. Heptane was added through the dropping funnel as required to maintain reflux at 219 F (104 C). After 4 hours of reflux, approximately 65 ml of aqueous distillate had been collected. The water from acrylation and heptane were withdrawn from the trap and the dry air flow was increased to about 56 liters per hour. When distillation stopped, additional heptane had collected in the trap.

The batch was cooled to 122 F (50 C) with a trickle of dry air. The acid no. of the product was 34.

POLYESTER 2 A hydroxy-terminated polyester was prepared in an identical fashion to that described for Polyester 1 with the following charge weights: 1, 6-Hexanediol 992.7 g Glycerine 133.5 g Phthalic anhydride 1071 g Dibutyltin bislauryl mercaptide 0.5 g The reaction mixture was cooled and water collected.

The final product had an acid no. of 2.4 and a hydroxyl no. of 179. Therefore, it had a hydroxyl equivalent weight of 316.

POLYESTER 3 A hydroxy-terminated polyester was prepared in an identical fashion to that described for Polyester 1 with the following charge weights: 1,6-Hexanediol 1058 g Isophthalic acid 356 g Glycerine 5 g Adipic acid 582 g Dibutyltin bislauryl mercaptide 0.4 g The reaction mixture was cooled and water collected.

The final product had an acid no. of 0.10 and a hydroxyl no. of 181. Therefore, it had a hydroxyl equivalent weight of 312.

WEARLAYER COATING COMPOSITION 1 A polyurethane floor covering wearlayer composition was prepared from the following charge in a 5 liter flask equipped with heating mantle, stirrer, and dry air purge at about 0.7 liters per hour: Polyester 3 1111 g Hexanediol diacrylate 341 g 2-Hydroxyethyl acrylate 409 g 2,6-Di-tert-butyl-4-methylphenol 0.72 g Dibutyltin bislauryl mercaptide 6.3 g 4,4-dicyclohexylmethane diisocyanate 96 g The flask was heated to 120 F (49 C) and the mixture exothermed. This mixture was held at 185 F (85 C) for a period of four hours and upon cooling to 140 F (60 C) the following materials were added: Acrylic acid 245 g Decyl acrylate 518 g 50/50 by wt. mixture of 1-cyclohexyl-68 g 1-hydroxyacetophenone and benzophenone Benzophenone 35 g Silicone surfactant 1.7 g WEARLAYER COATING COMPOSITION 2 A polyurethane floor covering wearlayer composition was prepared from the following charge in a 2 liter flask equipped with heating mantle, stirrer, and dry air purge at about 0.7 liters per hour: Hydroxyalkyl acrylate 126 g Monomer mixture of ethoxylated 125 g triacrylates Polyester 2 35 g The hydroxyalkyl acrylate used was sold by Union Carbide under the trademark Tone M-100. The monomer mixture was 27.5% by wt. SR-499,27.5% by wt. SR502 and 45% by wt. SR351. SR-499, SR502 and SR351 are trademarks for ethoxylated triacrylates sold by Sartomer. The mixture was heated to 100 F (36 C) and 87 grams of an isocyanurate ring compound based on hexamethylene diisocyanate sold by Bayer under the trademark Desmodur N-3300, were added. The mixture was heated to 185 F (85 C) and maintained at this temperature for five hours.

The mixture was cooled and to the flask were added: Monomer mixture of ethoxylated 15 g triacrylates Silicone surfactant 1 g The monomer mixture was the same as identified above. An infrared spectrum confirmed that all of the NCO groups had reacted.

WEARLAYER COATING COMPOSITION 3 A polyurethane floor covering wearlayer composition was prepared from the following charge in a 3 liter flask equipped with heating mantle, stirrer, and dry air purge at about 0.7 liters per hour: Polyester 2 180 g Hydroxyalkyl acrylate 666 g Isocyanurate ring compound 470 g This mixture was heated to 185 F (85 C) and maintained at this temperature for a period of four hours. The mixture was cooled slightly and to the mixture were added: Acrylated Polyester 1 524 g Acrylic acid 160 g An infrared spectrum confirmed that all of the NCO groups had reacted.

COMPARATIVE EXAMPLE 1 Wearlayer Coating Composition 1 was preheated to 110 F (43 C) to reduce the viscosity. The Coating Composition 1 was then applied onto a 33 cm wide, 76.2 micron thick, rigid vinyl web, by using a #30 rod at a line speed of 7.6 meters per minute. The web was routed over a 0.76 m diameter cooling drum having two 300 watt Fusion system H-bulb lamps mounted in the across machine direction over the rigid vinyl web. Curing Coating Composition 1 under these conditions resulted in distortion of the rigid vinyl film due to the temperature of the rigid film exceeding the glass transition temperature of 83 C. Sections of this film were wound onto a 15 cm internal diameter core.

An attempt was made to laminate this film onto a tile base and emboss it. A vinyl mixture sheet 1.0 to 1.1 mm in thickness was provided on the conveyor such as shown in Figure 4 at a temperature of 300-320 F (149-160 C). The belt was heated to enable good adherence of the sheet to the belt. This belt line consisted of two sets of rolls used for lamination and embossing processes. The coated film was fed into the first nip with the coated side against the laminator roll. The partially distorted ultra violet (W) cured coated film adhered to the laminator roll and did not release and laminate to the tile base. No acceptable tile product could be prepared by this method.

EXAMPLE 1 Wearlayer coating composition 1 containing no photoinitiator was applied at room temperature onto a 33 cm wide decorated rigid vinyl film, similar to the film of Comparative Example 1, by using a precision reverse three roll coater. The coating application yielded a 50 micron coating. This coated film was routed through an Energy Science Electro-Curtain machine operating at 125 KeV with a 7.0 cm average gap between the titanium electron beam window and the wearlayer/film composite at a line speed of 1.5 meters per minute. The dosage was 1.4 Mrad and the level of oxygen within the nitrogen inerted chamber where the coating was cured was kept below 50 parts per million. Color measurements were made on the cured film and the curing Delta b value computed based on the change in yellowness during cure of the composite rigid film was 1.0.

This material was processed using the belt line described in Comparative Example 1. A vinyl mixture sheet 1.0 to 1.15 mm in thickness was provided on a conveyor at a temperature of 300-320 F (149-160 C). The belt was heated to enable good adherence of the sheet to the belt. This belt line consisted of two sets of rolls used for the lamination and embossing processes. Each set of vertical rolls provided a nip through which the belt and rigid film/tile base were routed. The coated film was fed through the space between the rolls (nip) with the coated side against the laminator roll. In the first nip, the sheet and coated film are laminated together. The heat from the sheet raised the temperature of the coated rigid film above the glass transition temperature.

Shortly after being laminated, the sheet passed through a second nip where embossing of the coated vinyl film provided a surface effect. The temperature of the laminated sheet was maintained above the glass transition temperature of the film and the hardening point of the vinyl mixture sheet to allow for surface embossing.

EXAMPLE 2 Wearlayer Coating Composition 3 was applied onto a 33 cm wide decorative rigid film at a nominal thickness of 48 to 51 microns. The coated film was routed through an Energy Science Electro-Curtain machine operating at 125 KeV with a 7.0 cm average gap between the titanium electron beam window and wearlayer surface at a line speed of 1.5 meters per minute. The dosage was 3.6 Mrad and the level of oxygen within the nitrogen inerted chamber where the coating was cured was kept below 50 parts per million.

Color measurements were made on cured white decorated film and the Delta b value computed based on change in yellowness during coating and curing (at low accelerating energy of 125 KeV) of the composite rigid vinyl film. The curing Delta b value was 0.60. The final roll of precoated white, decorative rigid vinyl film was processed on the same type of belt line as described in Example 1.

EXAMPLE 3 Wearlayer Coating Composition 2 was applied onto a 33 cm wide decorative rigid film at a nominal thickness 1.0 to 1.15 microns. The coated film was routed through an Energy Science Electro-Curtain machine operating at 125 KeV with a 7.0 cm average gap between the titanium electron beam window and wearlayer surface at a line speed of 1.5 meters per minute. The dosage was 3.3 Mrad and the level of oxygen within the nitrogen inerted chamber where the coating was cured was kept below 50 parts per million.

Color measurements were made on the cured film and the Delta b value computed based on change in yellowness during coating and curing of the composite rigid vinyl film. The result was a curing Delta b of 1.21.

This coated rigid vinyl film was laminated to a vinyl mixture sheet using a belt line similar to that described in Comparative Example 1. The vinyl mixture sheet, 1.0 to 1.2 mm in thickness, was provided on a conveyor at a temperature of 300-320 F (149-160 C). The belt was heated to enable good adherence of the sheet to the belt. This belt line contained a single nip in which the same roll was used for both lamination and embossing steps. The coated film was fed through the nip with the coated side against the laminator roll. In the nip, the sheet and coated film were laminated and embossed together.

EXAMPLE 4 Wearlayer Coating Composition 3 was applied onto a decorative rigid vinyl film and cured by electron beam in a manner identical to that described in Example 3. In this example, a floor tile was formed on a 1.8 m diameter drum.

Referring to Figure 5, the vinyl mixture sheet 4 was fed onto conveyor 23 at a temperature of 300-320 F (149-160 C). The sheet 4 was transferred from conveyor 23 to the surface of the upper portion of the drum 24.

The drum surface was maintained at a temperature of 180 F (82 C) 30 F (17 C). At this drum temperature, good adherence of the vinyl mixture to the drum was achieved.

At about the 11 o'clock position (as shown in Figure 5) on the drum, the vinyl mixture was fed through the first nip formed by the laminator roll 26 and the drum roll 24. The coated decorative rigid vinyl film 15 with the wearlayer coated side against the laminator roll 26 met the vinyl mixture sheet 4 at the nip and film and sheet were laminated.

Then at about the 10 o'clock position, a second embossing roll 28 formed a nip with the drum 24 and provided an embossed effect on the surface of the precoated decorative rigid vinyl film.

At about the 9 o'clock position, water was sprayed onto the coated rigid film/sheet to cool the surface of the film to approximately 150 F (66 C). The coated film/sheet laminate passed through water bath 30 where the temperature was further reduced below the glass transition temperature of the rigid vinyl film. The laminate was then cut into tiles.

EXAMPLE 5 An experimental abrasion resistant 100% solids inorganic/organic (colloidal silica/acrylate) coating supplied by SDC Inc. of Anaheim, California, was applied at room temperature onto a 33 cm wide decorative rigid vinyl film with an offset gravure coater equipped with a smoothing bar. This coated film was routed through an Energy Science Electro-Curtain machine operating at 120 KeV at a line speed of 12 meters per minute. The dosage was 2 Mrad. The final cured coating thickness was approximately 12.7 microns. The roll of cured, precoated decorative rigid vinyl film was processed on the same type of belt line described in Example 1.

EXAMPLE 6 A wearlayer coating composition was prepared by mixing 70% by weight of Acrylated Polyester 1 with 30% by weight of a trifunctional ethoxylated acrylate sold by Sartomer under the trademark SR9035. This coating composition was applied at room temperature onto a 30 x 30 cm decorative rigid vinyl film with a wire wound rod.

This coated film was routed through an Energy Science Electro-Curtain machine operating at 120 KeV at a line speed of 7.5 meters per minute. The dosage was 2 Mrad.

The final cured coating thickness was approximately 38 microns. The roll of cured, precoated decorative rigid vinyl film was processed into a tile using a heated press with a 30 x 30 cm tile embossing plate.

EXAMPLES 7 to 9 To illustrate the effect of electron beam penetration on the final color of the white pigmented decorative rigid vinyl film, Wearlayer Coating Composition 3 was applied onto 71 to 76 micron decorative rigid vinyl film in a manner identical to that described in Example 3 and electron beam cured at different accelerating energies while maintaining the same dosage of 3.3 Mrad. The cured coated film sections were analysed for color variation by utilizing a Minolta Colorimeter. Tristimulus color values are summarized as Delta b for each of the examples: KeV Mrad Delta b Example 7 125 3.3 0.94 Example 8 130 3.3 1.81 Example 9 135 3.3 2.25 Electron beam curing at an electron beam accelerating energy of 125 KeV did not result in any significant yellowing of the coated white decorative film as indicated by the Delta b value of 0.94 in Example 7. Increasing the accelerating energy to 130 KeV resulted in slight yellowing of the decorative film as evident by a 100% increase in the Delta b value to 1.81 for Example 8. Electron beam curing the coated film at an accelerating voltage of 135 KeV in Example 9 resulted in objectionable yellowing of the decorative film in comparison to the 125 KeV processed sample, e. g., 0.94 versus 2.25 at 135 KeV.

Claims (27)

CLAIMS :

1. A process of making a surface covering comprising the steps of : a. providing a sheet of vinyl film material, b. coating the sheet with a wearlayer composition comprising a cross-linkable

organic moiety, and c. curing the wearlayer composition with electron beam radiation, the electron beam radiation having an energy level of less than 135 KeV with a 7.0 cm average gap.

2. The process of claim 1, wherein the electron beam radiation has an energy level of at least 100 KeV with a 7.0 cm average gap.

3. The process of claim 1 or claim 2 wherein the wearlayer composition is subjected to 2 to 4 Mrad of electron beam radiation.

4. The process of any one of claims 1 to 3, further comprising laminating the cured wearlayer/film composite to a substrate.

5. The process of claim 4, wherein the composite is embossed.

6. The process of any one of claims 1 to 5, wherein the energy level of the electron beam radiation is no greater than 130 KeV with a 7.0 cm average gap.

7. The process of any one of claims 1 to 6, wherein the film has a curing Delta b of no greater than 2 when measured before and after curing of the wearlayer composition.

8. A process of making a surface covering, substantially as described with reference to and as illustrated by one of or more of the Figures in the accompanying drawings.

9. A process of making a surface covering, carried out substantially as described in any one of Examples 1 to 8 herein.

10. A surface covering comprising a wearlayer/film composite, the wearlayer comprising a composition including a cross-linked organic moiety, the film comprising a vinyl composition, the film having a thickness of no greater than about 0.5 mm, the wearlayer composition having been cured with electron beam radiation, and the film having a product Delta b of no greater than 2 as measured by the difference between the +b (yellow) value of the wearlayer/film composite on a calibration plate and the +b (yellow) value of the calibration plate alone.

11. A surface covering comprising a wearlayer/film composite, the wearlayer comprising a composition including a cross-linked organic moiety, the film comprising a vinyl composition, the film having a thickness of no greater than about 0.5 mm, the wearlayer composition having been cured with electron beam radiation, and the film having a Delta b of no greater than 2 as measured before coating of the wearlayer composition and after curing of the wearlayer composition.

12. The surface covering of claim 10 or claim 11, in which the film has a Delta b of no greater than 1.

13. The surface covering of any one of claims 10 to 12, wherein the wearlayer organic moiety prior to cross-linking is an ethylenic moiety, an epoxide moiety, or a mixture of such moieties.

14. The surface covering of claim 13, wherein the moiety is an acrylic moiety.

15. The surface covering of any one of claims 10 to 14, wherein the wearlayer composition comprises an acrylated urethane.

16. The surface covering of any one of claims 10 to 15, wherein the wearlayer has a thickness of 25 to 76 microns.

17. The surface covering of any one of claims 10 to 16, wherein the film has a thickness of less than about 0.25 mm.

18. The surface covering of claim 17 wherein the film has a thickness of 25 to 76 microns.

19. The surface covering of any one of claims 10 to 18, wherein the film is a rigid vinyl film.

20. The surface covering of any one of claims 10 to 19, wherein the film is capable of yellowing to an extent giving a curing Delta b value greater than 2.

21. The surface covering of any one of claims 10 to 20, wherein the double bond conversion of the wearlayer composition upon curing is at least 75%.

22. The surface covering of any one of claims 1 to 21, in the form of a sheet, the product Delta b across the width of the sheet being less than 1.

23. A surface covering whenever made by a process as claimed in any one of claims 1 to 9.

24. A surface covering substantially as described in any one of Examples 1 to 8 herein.

25. The surface covering of any one of claims 10 to 24, which is laminated to a substrate.

26. The surface covering of claim 25, wherein the composite is embossed.

27. Any new feature disclosed herein or any new combination of hereindescribed features.