GB2071121A - Method and apparatus for producing a surface covering having reduced surface gloss and surface covering produced thereby - Google Patents

Abstract

This invention pertains to a method and apparatus for producing a cured resinous coating which exhibits a reduced gloss level. In a preferred embodiment, the cured resinous coating which exhibits a reduced gloss level is a wear resistant coating and is superimposed on a resilient floor covering material. The gloss level is reduced by subjecting the coating to corona discharge before it is cured. The curing process is achieved at least partially by irradiation of the coating and may additionally involve some moisture-curing.

Description

SPECIFICATION Method and apparatus for producing a surface covering having reduced surface gloss, and surface covering produced thereby This invention relates to coatings which are at least partially curable by radiant energy, and to the resulting cured coatings.

More specifically, this invention relates to a method and apparatus for reducing the surface gloss exhibited by the cured coatings.

In one of its more specific aspects, this invention concerns a corona discharge method and apparatus fortreating liquid, uncured coatings to reduce the surface gloss exhibited by the coatings when cured.

The resilient flooring industry has done much work pertaining to the development of high gloss wear layer coatings which are curable by radiant energy or a combined radiant energy and moisture cure. These coatings provide abrasion resistance and impart a high gloss appearance to floor coverings. The abrasion resistance provided by these coatings is always a desirable property; however, the high gloss appearance is not, especially in heav ilytrafficked areas of a floor, since maintenance time is increased. Accordingly, the flooring industry is continually searching for ways to control the gloss levels of these coatings.

Prior art methods of reducing gloss or flatting typically involve the employment of various particulate flatting agents in the wear coating compositions.

The use of flatting agents has been generally unsatisfactory since their use results in deglossed coatings which exhibit a reduction in other physical properties. Another method known in the art is steam deglossing. (See U.S. Patent No. 4,197,344).

According to this invention there is provided a method for producing a radiant energy cured resinous coating having a reduced gloss level which comprises coating the surface of a substrate with a liquid resinous coating composition curable by radiant energy; treating at least a portion of the surface ofthe liquid resinous coating with a corona discharge sufficient to reduce the gloss level of the coating in the treated portion; and exposing the liquid resinous coating having a reduced gloss level to a dosage of radiant energy sufficient to polymerize the coating and set the reduced gloss level.

Also according to this invention there is provided a method for producing a combined radiant energy and moisture cured resinous coating having a reduced gloss which comprises coating the surface of a substrate with a liquid resinous coating composition curable by a combined radiant energy and moisture cure; treating at least a portion of the surface of the liquid resinous coating with a corona discharge sufficient to reduce the gloss level of the coat ing in the treated portion; exposing the liquid resinous coating having a reduced gloss level to a dosage of radiant energy sufficient to polymerize the radiant energy curable components of the coating and set the reduced gloss level; and subjecting the radiant energy cured coating to a moisture cure to fully cure the coating.

The present invention also provides an apparatus for producing a cured resinous coating which comprises: (a) means for coating the surface of a substrate with a liquid resinous coating composition at least partly curable by radiant energy; (b) means for treating at least a portion of the surface of the liquid resinous coating with a corona discharge sufficient to reduce the gloss level of the coating in the treated portion; and (c) means for curing the liquid resinous coating whereby the corona discharge treated portion of the cured coating exhibits a reduced gloss level.

As indicated above, the coating may be, for example, curable fully by radiant energy or partly by radiant energy and partly by moisture. The curing means will be that appropriate for the coating in question. The apparatus may therefore comprise, for example, means for curing the radiant energy curable components of the liquid coating; and means for curing the moisture curable components of the radiant energy cured coating whereby the corona discharge treated portion of the fully cured coating exhibits a reduced gloss level; it will be appreciated, however, that moisture-cure can be effected by subjecting the partly cured material to a period in atmospheric air.

The coatings to be subjected to corona treatment according to this invention are in liquid form and are broadly classified as resinous coating compositions which are curable by either radiant energy or by a combined radiant energy and moisture cure.

Resinous coating compositions curable by radiant energy which are suitable for use in this invention include compositions that are polymerizable by reactions that are initiated by free radicals, such compositions being described herein as free radical initiated polymerizable compositions and include free radical initiated ethylenically unsaturated polymerizable compositions, and free radical initiated polyene polythiol polymerizable compositions. Particularly suitable free radical initiated ethylenically unsaturated polymerizable compositions include urethane acrylates and acrylated polyesters.

Also suitable for use in this invention are resinous compositions curable by a combined radiant energy and a moisture cure such as the liquid urethane acrylate coating compositions taught in U.S. Patent No.

4,138,299 to N.C. Bolgiano. If a combined radiant energy and moisture curable resinous coating composition is employed in the practice of this invention, it should advantageously contain a radiant energy curable content of at least 5%. Preferably, 30 to about 40% of the coating composition will be curable by radiant energy. The present invention, using a coating produced according to U.S. Patent No.

4,138,299, is demonstrated in Example 41.

The coating compositions may contain additives, for example, heat and light stabilizers, fillers, or pigments, many of which are known in the art, in appropriate proportions.

In the accompanying drawings: Figure 1 is a graphic representation of the data of Table Figure 2 is a graphic representation of the data of Tables.

Figure 3 illustrates, by way of example only, one form of apparatus suitable for carrying out the method of the invention, and constructed in accordance with the invention.

Referring now to Figure 3, there is shown material to be coated 1, carried on means for moving 2, driven by drive means 3.

The material to be coated, after passing under means for coating 4 where a liquid resinous coating composition is applied, is passed through corona discharge region 5 existing in the gap between electrodes 6 and ground plate electrode 7 of corona discharge means 8. As the coated material passes through corona discharge region 5 the coating is the ated with a corona discharge sufficient to degloss the coating. The coated material exits from corona discharge means 8 and passes under curing means 9 where the treated coating on the material is bulk cured.

A material to be coated 1, in this instance, a commercial filled vinyl floor tile to be wear layer coated, is fed along a th2 inch (0.8 mm) thick silicone-rubber conveyor belt 2, the tile first passes under a conventional curtain applicator4where an ultraviolet light curable wear layer coating composition is applied to a thickness of about 6 mils (0.15 mm). The siliconerubber conveyor belt serves as a buffer dielectric for corona treatment. However, instead of a siliconerubber belt, any conventional nonconductive con veyorsystem can be employed.Instead of a curtain applicator, other conventional coating applicators, for example a roll coater, blade coater, spray coater, screen printer and the like can be employed to apply coating compositions to desired thicknesses, typically, within the approximate range of from 0.5 to 20 mils (about 0.013 to 0.5 mm).

Tile 1, which now has a 6 mil (0.15 mm) thick wet, uncured coating on its surface is fed through the gap existing between the bottom of electrodes 6 and the top ground plate electrode 7 at a conveyor speed within the approximate range of from 5 to 100 feet per minute (about 1.5 to 30 metres per minute). In this instance the ground plate electrode was positioned beneath the silicone-rubber belt, the belt passing over the top surface of the ground plate, as shown in Figure 3. The gap between the bottom of the electrodes 6 and the coating surface on the tile was about 0.124 inch (3.15 mm). Gap settings within an approximate range of from 0.02 inch to 0.25 inch (about 0.5 to 6.35 mm) have been found suitable for deglossing coatings according to this invention.

Alternatively, if only a portion of the surface of the coating isto be deglossed, a movable nonconductive mask or shield could be placed on the coating surface such that as the masked coating passes under the corona discharge means only a portion of the surface of coating is treated.

As the corona discharge means 8, use can be made of any unit capable of generating and sustain ing the treatment levels needed to degloss coatings, many such units being commercially available. A star electrode corona treater designated 'Softal Treater" available from Softal Corporation of America was found suitable for use but exhibited a tendency to arc at high power levels and used considerable amounts of gas.

Particularly suitable for use and preferred in the practice of this invention is the corona discharge device described in co-pending applications Case Nos. 128,539 and 128,540 filed today, the disclosures of which are incorporated herein by reference and to which the reader is referred for more detailed information. The particular corona discharge device employed in the practice of this invention consisted of two, 29 inch (0.74 m) long, 1/4 inch (6.35 mm) O.D.

copper tube electrodes, each encased in 30 inch (0.76 m) long qua rtz tubes having outside diameters of 0.6 inch (150 mm) and wall thicknesses of 0.04 inch (1 mm), and one aluminium ground plate electrode about 5 inches (13 cm) long and 14 inches (36 cm) wide. The copper tube electrodes were positioned immediately adjacent and parallel to each other at a centre line separation of about 2 inches (5 cm), and the aluminium ground plate electrode was positioned parallel to and a spaced distance from the copper tube electrodes beneath the surface of the silicone-rubber belt carrying the tile.Shrouding the copper tube electrodes was a glass fiber reinforced silicone housing which defined a gas plenum chamber and served to direct an inlet gas or gas mixture, to be ionized, perpendicularto the lengthwise direction of the electrodes and into the gap or corona discharge region. As described in the above-referenced application, the housing serves to provide a corona discharge characteristic of the inlet gas which in this instance was nitrogen. The gas is introduced into the housing at a flow rate of from about 10 to about 45 liters per minute per electrode.

As this gas flows into the corona discharge region to be ionized, it serves to force away all contaminating gases. In the case of most ultraviolet radiation curable wear resistant coatings for flooring, contaminating gases include air and oxygen, which inhibit the cure of these coatings. In the operation of the Rueggeberg corona discharge device, to optimize the corona activity of the gas to be ionized, a liquid buffer dielectric/coolant, for example, hydrocarbon or mineral transformer oils, ethylene glycol, or glycerine, circulates through the cylindrical passageway created between each coppertube electrode and quartz tube at an average velocity flow of from about 20 to 30 inches (0.5 to 0.75 m) per set ond. Typically, the dielectric/coolant is circulated at the rate of about 1 U.S. gallon per minute (3.8 liters per minute).

Selection of a gas or gas mixture employed in the operation of the corona discharge device has a considerable effect on the amount of deglossing achieved. The gas employed affects the activity and uniformity of the corona discharge and, accordingly, the uniformity and amount of deglossing of the coating. The gas is introduced into the active corona reg ion and ionized forming a corona discharge for treated ing the coating surface. Furthermore, as indicated above, if the cure of the coating is oxygen-inhibited, another purpose of the gas is to provide an inert atmosphere.Typically, these oxygen-inhibited coatings exhibit little deglossing when corona treated in an atmosphere containing a detectable amount of more than about 0.1% oxygen as compared to the amount of deglossing they exhibit in atmospheres containing about 0.1% or less oxygen.

Any suitable gas or gas mixture can be employed.

Gases and gas mixtures which have been employed and found suitable for use in this invention include argon, carbon dioxide, nitrogen, helium, nitrous oxide, tetrafluoromethane, sulfur hexafluoride, argon and carbon dioxide, argon and helium, argon and nitrogen, argon and nitrous oxide, and helium and carbon dioxide. It has also been found that a gas or gas mixture containing water vapor at more than about 25% relative humidity produces a smoother corona and a smoother texture on the deglossed surface.

Argon or helium has been found to provide the most deglossing for the coating of Example I. This is believed to be because both gases are very easily ionized.

After corona treatment the tile is conveyed under curing means 9 which in this instance was a bank of ultra-violet lights directing sufficient radiant energy on the coating to completely polymerize it. If the liquid resinous coating composition is curable by a combined radiant energy and moisture cure, curing means 9 will be supplemented by a subsequent moisture cure which can consist of allowing the coating to age at room conditions as taught in U.S.

Patent No. 4,138,299.

The degree of deglossing, the rate of deglossing, and the tendency to regloss after corona treatment and before bulk cure of a particular coating type have been found to be affected by coating composition additives, photoinitiators, coating viscosity, and coating thickness. Accordingly, the optimum conditions for deglossing a particular coating can be determined only by experimentation. For example, it has been found possible to degloss the coating of Example I without the use of a photoinitiator. This is believed to be explained by the fact that free radicals are formed by the corona treatment, thus directly initiating the cure mechanism. Table III (below) shows the effect viscosity has on deglossing the coating of Example I.Furthermore, it has been found that if reglossing of a coating after corona treatment is a problem, it is necessary to bulk cure the treated coating immediately upon its exit from the corona treater. However, if reglossing is not a problem, the time between corona treatment and bulk cure is not critical. Also, it has been found that the degree of deglossing achieved is inversely proportional to the coating thickness.

The above findings are provided as broad guidelines to be considered when practicing this invention. The Tables below, set forth and demonstrate in detail the parameters of this invention in relationship to the coating of Example The following Examples illustrate the invention: There will first be described the preparation of a free radical initiated ethylenically unsaturated polymerizable composition used to produce the data set forth in Tables I-V below, this being designated Example I.

About 21.9 weight percent of 4,4' diisocyanato dicyclohexylmethane, about 0.05 weight percent 2,6 - di - tert - butyl - 4 - methylphenol, about 0.2 weight percent 2 - ethylhexyl acrylate, and about 0.1 weight percent of dibutyltin dilaurate catalyst were introduced into a reaction vessel with agitation.

About 7.2 weight percent 2 - ethylhexylacrylate and 10.8 weight percent hexanediol diacrylate were introduced into the reaction vessel with agitation.

The contents of the reaction vessel were agitated for about 10 minutes and about 6.8 weight percent 2 - hydroxyethyl acrylate was added to the contents of the reaction vessel at a rate such that the temperature in the reaction vessel did not exceed 1300F (54"C).

About 2.2 weight percent 2 - ethylhexyl acrylate was introduced into the reaction vessel and the temperature of the reaction vessel was held at 1300F (54 C) for about one hour.

The reactor was cooled to about 1200F (49"C) and about 17.7 weight percent of the reaction product and 1 mole glycerol, 3 moles of a 7/3 mixture of adipic acid and isophthalic acid and 3 moles of 1,6 hexanediol (Hooker Chemical Trio I F-2039-1 80, MW 960, Hydroxyl No. 175) was rapidly added to the reactor contents. The temperature in the reaction vessel was not allowed to exceed 140"F (60"C).

Next, about 16.6 weight percent of a polycaprolactone diol (Union Carbide PCP-0200 diol, MW 540, Hydroxyl No. 207) was added to the contents of the reaction vessel and the temperature of the vessel was cooled to about 140"F (60"C).

About 2.2 weight percent 2 - ethylhexyl acrylate was added to the reaction vessel and the temperature of the vessel was held at about 140"F (60 C) for about four hours.

The temperature of the reaction vessel was cooled to about 90-100 F (32-38"C) and about 6.7 weight percent acrylic acid was added to the reaction vessel.

Into a mix tank were added about 2 weight percent benzophenone, about 0.1 weight percent glycol polysiloxane (Dow Corning DC-193), and about 2.2 weight percent 2 - ethylhexyl acrylate with agitation.

The contents of the mix tank were added to the reaction vessel.

About 1.0 weight percent of benzoinisobutylether was added to the reaction vessel followed by about 2.2 weight percent 2 - ethylhexyl acrylate.

The contents of the reaction vessel were agitated to ensure complete dispersion of all ingredients and the resulting product was recovered as a free radical initiated ethylenically unsaturated polymerizable liquid coating composition suitable for use in the practice ofthis invention. The composition was tested and found to have a viscosity of 28,000 cps at 25"C (Brookfield LVF, Spindle #J b! )))$) The various parameters which affect the amount of deglossing achieved using the method and apparatus of this invention are illustrated below in Tables I through VI.All samples to be treated were prepared in the same manner, that is, 40 filled vinyl floor tiles were wear layer coated with the composition of Example lto a thickness of about 6 mils (0.15 mm). The tiles of Examples 40,41, and 43 were coated with 6 mils (0.15 mm) of the specified coating compositions. All samples, other than the controls, were subjected to corona discharge treatment using the corona discharge device described above. After corona treatment, all samples were bulk cured using a bank of ultraviolet lights and tested for gloss levels using a 60 Gardner glossmeter.

In the Tables, flow rates in galls per minute are in U.S. gallons, and may be approximately converted to liters per minute by multiplying by 3.8.

Line speeds are in feet per minute, and may be approximately converted to meters per minute by multiplying by 0.305.

Treatment levels are in watt-min/ft2, and may be approximately converted to watt-min/m2 by multiplying by 10.8.

Distances given in inches may be converted to millimetresby multiplying by 25.4.

TABLE I Deglossing Achieved at Various Treatment Levels Constants: dielectric/coolant = transformer oil (1 gal/min) (Examples 1-8) ethylene glycol (1 gallmin) (Examples 9-15) gap = 0.124 inch Gas or Gas Line Power Treatment Example Mixture Speed In put Level' Gloss No. (liters/min) (fpm) (watts) (watt-min/ft) (60 ) Control (untreated) 95 1 Ar(49) & C02(5) 40 108 2.5 85 2 Ar(49) & O2(5) 40 216 5 85 3 Ar(49) & O2(5) 20 216 10 63 4 Ar(49) & CO2(5) 20 432 20 60 5 Ar(49) & O2(5) 10 432 40 42 6 Ar(49) & O2(5) 10 864 80 25 7 Ar(49) & O2(5) 10 1080 100 40 8 Ar(49) & O2(5) 5 864 160 12 9 N2(54) 100 800 7.4 90 10 N2(54) 80 800 9.2 87 11 N2(54) 60 800 12.3 72 12 N2(54) 40 800 18.5 25 13 N2(54) 20 800 36.9 28 14 N2(54) 10 800 73.9 3 15 N2(54) 5 800 147.7 5 Treatment Level = Pa x N = watts x minutes dxVm = ft Pa = power per electrode (watts) N = number of electrodes d = active corona length per electrode (feet) Vm = line orconveyorspeed (feet/minute) TABLE II Deglossing Achieved Using Different Liquid Buffer DielectriclCoolants Constants: gas mixture = Ar (48.6 1/min) & CO2 (5.4 l/min.) line speed = 10 fpm power input = 800 watts gap = 0.124 inch treatment level = 73.9 watt-min/ft2 Example DielectriclCoolant Gloss No. (Flow Rate in gallmin.) 660 ) Control (untreated) 94 16 ethylene glycol (1) 20 17 transformer oil (1) 40 TABLE III Deglossing Achieved by Varying Coating Composi tion Viscosity by Adding Ethylhexyl acrylate Constants:: dielectnc/coolant = transformer oil (1 gal/min) gap = 0.124 inch gas mixture = Ar (48.6 1/min) & CO2 (5.4 l/min.) power input = 500 watts line speed = 10 fpm treatment level = 46.3 watt-min/ft.2 Viscosity at 25 C Example (Brookfield LVF Spindle Gloss No. #4,20 rpm) (60 ) Control No adjustment (28,000 cps) 30 18 to 16,400 cps 35 19 to 10,200 cps 20 TABLE IV Deglossing Achieved by Varying Gap Between Elec trode and Coating Surface Constants: dielectric/coolant = ethylene glycol (1 gal/min) gas = N2 (54 1/min) power input = 600 watts line speed = 10 fpm treatment level = 55.5 watt-min/ft2 Example Gap Over Coating Gloss No. (Inches) (60"1 20 0.040 4 21 0.073 5 22 0.104 14 23 0.136 47 24 0.167 66 25 0.200 65 TABLE V Deglossing Achieved Using Different Gases Constants: dielectric/coolant = transformer oil (1 gal/min) line speed = 10 fpm gap = 0.124 inch power input = 500 watts treatment level = 46.3 watt-min./ft2 Example Gas or Gas Mixture Gloss No. (llminJ (60) Control (untreated) 95 26 Ar(54) 3 27 CO2(54) 35 28 N2(54) 7 29 He(54) 3 30 N2O(54) 57 31 CF4(54) 62 32 Ar(49) & CO2(5) 37 33 He(27) & CO2(27) 45 34 Ar(49) & He (5) 3 35 Ar(49) & N2O(5) 85 36 Ar(49) & CF4(5) 3 37 Ar(49) & N2(5) 3 38 N2(49) & Ar(5) 5 39 Ar(54) & SF6(2.7) 75 TABLE Vl DeglossingAchievedhy Using Different Coating Types Constants: dielectric/coolant = ethylene glycol (1 gal/min) line speed = 10 fpm Gas or Gas Power Treatment Example Coating Type & Mixture Input gap Level Gloss No. (Cure Mechanism) (llters/min) (Watts) (inch) (Watt-min/. lt2) (600) 40 polyene-polythioll (uv) Ar(54) 700 0.192 64.8 5 41 urethane acrylate2 (uv-moisture) Ar(54) H20 625 0.056 62.5 5 vapor 8 42 urethane acrylate3 (uv) Ar(49) CO2 (5) 500 0.124 46.3 32 43 acrylate polyester (uv) Ar(49) CO2(5) 500 0.124 46.3 50 1 coating of Example I, U.S.4,150,169 2 coating of U.S. 4,138,299 (40% radiant energy/60% moisture curable) 3 coating of Example I * at more than 25% Relative Humidity It will be seen from the data set forth in Tables l-VI that by varying the various conditions, one is able to control the level of deglossing achieved using the method and apparatus of the present invention.

Claims (13)

1. A method for producing cured resinous coating which comprises: (a) coating the surface of a substrate with a liquid resinous coating composition at least partly curable by radiant energy; (b) treating at least a portion of the surface of the liquid resinous coating with a corona discharge sufficient to reduce the gloss level of the coating in the treated portion; and (c) exposing the liquid resinous coating having a reduced gloss level to radiant energy sufficient to polymerize the coating and set a reduced gloss level.

2. The method of claim 1 in which said liquid resinous coating composition is a free radical initiated ethylenically unsaturated polymerizable coating composition fully curable by ultraviolet light.

3. The method of claim 1 in which said liquid resinous coating composition is a free radical initiated polyene-polythiol polymerizable coating composition fully curable by ultraviolet light.

4. A method for producing a combined radiant energy and moisture cured resinous coating which comprises: (a) coating the surface of a substrate with a liquid resinous coating composition curable by a combined radiant energy and moisture cure; (b) treating at least a portion of the surface of the liquid resinous coating with a corona discharge suf ficientto reduce the gloss level of the coating in the treated portion; (c) exposing the liquid resinous coating having a reduced gloss level to a dosage of radiant energy sufficient to polymerize the radiant energy curable components of the coating and set a reduced gloss level; and (d) subjecting the radiant energy cured coating to a moisture cure to fully cure the coating.

5. The method of claim 4 in which said liquid resinous coating composition is a free radical initiated ethylenically unsaturated polymerizable coating composition curable by a combined radiant energy and moisture cure.

6. The method of claim 4 or claim 5 in which the radiant energy is ultraviolet light and the moisture cure comprises allowing the coating to age at room conditions.

7. The method of any one of claims 1 to 6 in which said corona discharge is produced by ionizing a gas or gas mixture which contains water vapor at more than about 25% relative humidity.

8. The method of any one of claims 1 to 6 in which said substrate is a resilient floor covering material and the coating composition is a wear layer-forming coating composition.

9. The method of claim 1, carried out substantially as described in any one of the Examples herein.

10. Apparatus for producing a radiant energy cured resinous coating which comprises: (a) means for coating the surface of a substrate with a liquid resinous coating composition at least partly curable by radiant energy; (b) means for treating at least a portion of the surface of the liquid resinous coating with a corona discharge sufficient to reduce the gloss level of the coating in the treated portion; and (c) means for fully curing the liquid resinous coating whereby the corona discharge treated portion of the cured coating exhibits a reduced gloss level.

11. Apparatus for producing a combined radiant energy and moisture cured resinous coating which comprises: (a) means for coating the surface of a substrate with a liquid resinous coating composition curable by a combined radiant energy and moisture cure; (b) means fortreating at least a portion of the surface of the liquid resinous coating with a corona discharge sufficientto reduce the gloss level of the coating in the treated portion; (c) means for curing the radiant energy curable components of the liquid coating; and (d) means for curing the moisture curable compo nexts of the radiant energy cured coating whereby the corona discharge treated portion of the fully cured coating exhibits a reduced gloss level.

12. Apparatus as claimed in claim 10, substantially as described with reference to and as illustrated by Figure 3 of the accompanying drawings.

13. A coated substrate whenevar prepared by a method as claimed in any one of claims 1 to 9 or on an apparatus as claimed in any one of claims 10 to 12.