GB1589280A

GB1589280A - Coating process

Info

Publication number: GB1589280A
Application number: GB3169477A
Authority: GB
Original assignee: Monsanto Europe NV SA
Current assignee: Bayer Agriculture BVBA
Priority date: 1978-05-24
Filing date: 1978-05-24
Publication date: 1981-05-07

Description

(54) COATING PROCESS (71) We, MONSANTO EUROPE S.A., a Belgian Company, of Avenue de Terveren, 270--272, 1150 Bruxelles, Belgium, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a process useful in the production of surface covering materials, for example materials for covering floors or walls, or of artificial leather cloth, from vinyl chloride polymers.

Processes for the production of such materials are well known, a common feature being the application to a substrate of a coating of a vinyl chloride polymer in the form of a plastisol which is subsequently gelled by heating. Various methods for aplying the plastisol to the substrate have been proposed, depending on whether the coating is to be continuous or discontinuous.

For continuous coatings, application may, for example, be by curtain coating or by a spreader in conjunction with a doctor blade.

For discontinuous coatings, where the plastisol is to be applied to selected areas of the substrate, application of the plastisol by rotary screen printing has been proposed.

The use of a rotary screen having an allover mesh has also been proposed for the application of continuous plastisol coatings, and this can have advantages over other methods if the manufacturer already has rotary screen printing equipment installed.

In the production of certain types of surface covering materials, it would be desirable to apply a thicker continuous layer of plastisol than has hitherto been possible by rotary screen printing. For example it is generally considered necessary, in order to obtain a continuous layer having a thickness greater than 0.3 mm, to apply the plastisol in two or more coatings, usually with gelation of the first coating before application of the second and so on.

By the process of the present invention it is possible to apply to a substrate a continuous coating of plastisol having a thickness greater than 0.3 mm, specifically from 0.35 to 1.0 mm, in a single stage.

In the process of the present invention, a plastisol of a vinyl chloride polymer is applied to a substrate using a rotating cylindrical metal screen having a substantially uniform distribution of apertures, the outer surface of the screen being in contact with a continuously moving sheet of substrate, by supplying the plastisol to the interior of the cylinder wherein there is located constriction or scraper means such that the plastisol is forced through the apertures of the screen and on to the substrate, the process being characterised in that the screen has a thickness of at least 0.20 mm, the total area of the apertures (hereinafter referred to as the open area of the screen) is at least 25% of the total area of the screen, and the rates of supplying the plastisol to the cylinder, passage of the plastisol through the apertures and rotation of the cylinder being such that the coating of plastisol formed on the substrate by coalescence of the individual initially applied spots of plastisol has a thickness of from 0.35 to 1.0 mm.

The apertures in the screen may be curvelinear, for example circular, but are preferably polygonal, e.g. in the form of parallelograms or hexagons. The construction of the screen is preferably such that the apertures are polygons of uniform size and shape located at regular intervals in rows, such that adjacent edges of adjacent apertures are parallel and such that on a median line drawn through a row of apertures, the distance separating the adjacent parallel edges of two adjacent apertures i.e.

the width of an individual strand of the metal mesh, is not greater than the distance across an aperture. The distance across an aperture may be for example from 1.1 to 5 times the width of a strand of the metal mesh. Actual sizes of the apertures may, for example, range from 0.5 to 3 mm, a preferred range of aperture sizes (distance across on the median line) being from 1.0 to 2.0 mm. The percentage open area of the screen will of course vary with the relative widths of the apertures and the strands of metal mesh, but it preferably at least 35%, and may be as high as 75%.

A screen suitable for use in the present invention, and other apparatus including the screen, are illustrated diagrammatically in Figures 1 and 2 of the accompanying drawings, of which Figure 1 shows a portion of the screen structure, and Figure 2 shows a cross section of the screen, associated apparatus, and substrate.

Figure 1 shows a small area of a screen having hexagonal apertures 1, the body of the screen being formed by a network of metal strips 2, the width (b) of each strip on the median line A-A of a row of apertures being less than the width (a) of an aperture on the same line.

With reference to Figure 2, a cylindrical screen 3 is supported by means not shown and is driven via a toothed drive wheel (not shown) fitted over one end of the cylinder.

A tube 4, open at one end and closed at the other, is mounted wihin the cylinder and projects beyond the cylinder at each end.

The tube has a row of perforations at 5, the length of the row being substantially the same as the length of the cylinder.

Attached to the tube 4 is one edge of a flexible rectangular blade 6, the opposite edge of which is in contact with the interior wall of the cylindrical screen substantially along the entire length of the screen. The pressure of the blade 6 on the interior wall of the screen and also the angle of contact of the blade with the wall are adjustable.

A continuous substate sheet 7 passes between cylindrical screen 3 and a back roller 8, and is arranged to be substantially tangential to the outer wall of the screen along a line substantially coincidental with the line of contact of the edge of the flexible blade 6 with the inner wall of the screen.

In operation, a plastisol is fed to the tube 4 through its open end and discharged through the perforations 5 into the interior of the screen 3. As the screen 3 rotates in the direction of the arrow, the plastisol is carried round to form a bank of plastisol 9, the leading edge of which is located in the zone where the blade 6 is in contcat with the interior wall of the screen.

Pressure of the blade 6 on the leading edge of the bank forces the plastisol through the apertures in the screen and on to the substrate. Initially the deposit of plastisol is in the form of separate spots 10 corresponding to the individual apertures of the screen, but the spots rapidly coalesce to form a continuous coating 11 of substantially uniform thickness.

A tray 12 is placed below the screen to collect drips of plastisol.

Figure 2 shows an arrangement where the substrate is travelling vertically during printing with the plastisol, but the process of the invention is also applicable to processes wherein the substrate is horizontal or cQntacts the cylindrical screen at an angle between horizontal and vertical. Other constriction or scraper means which are alternatives to the flexible blade 6 may also be used; for example when using horizontal printing, a steel roller or rod which is attracted by a magnet towards the inner wall of the screen along a line substantially coincidental with the line of contact of the substrate with the outer wall of the screen, the magnet being located on the under side of the substrate, can be used to provide constriction means.

Substrates which can be used in the process of the invention include support materials which are retained in the structure of the finished floor- or wall-covering materials, and which may be, for example, fibrous webs such as non-woven fabrics and paper, woven fabrics and preformed films.

Examples of suitable support materials include asbestos paper, a material in which asbestos fibres are bonded with synthefic rubber, woven glass fibre, fabrics and glass fibres bonded with synthetic resins.

The process of the invention can be used to apply a continuous coating of plastisol as the first layer adjacent to the support material in a multilayer product, or it may be used to apply a continuous coating, for example to provide a wear layer, over one or more previous continuous or discontinuous layers.

In another application of the process of the invention, the plastisol is applied as a continuous coating to a support material which is intended to be stripped from the product after the gelation and curing of the thus-applied plastisol and of any subsequent layers deposited on the first continuous coating. After stripping of the support material, the vinyl chloride polymer layer derived from the first-deposited plastisol coating thus serves as a backing layer for the finished goods. The method of the invention is of particular value in such an application where a relatively thick polymer layer is desirable. Strippable support materials which can be used include siliconetreated papers.

The vinyl chloride polymer useful in the present invention can be a homopolymer of vinyl chloride or a copolymer of vinyl chloride with one or more other monomers copolymerisable therewith, for example vinyl acetate or vinylidene chloride. Preferred copolymers are those wherein at least 40% by weight of the copolymer is derived from the vinyl chloride.

Suitable plasticizers for use in preparing the plastisols include phthalates, for example alkyl benzyl phthalates such as butyl benzyl and octyl benzyl phthalate, and blends of phthaiates with modifiers. Also suitable are alkyl diaryl phosphates.

The plastisol used in the process of the invention is formulated to have suitable viscosity and other rheological characteristics and good, gelation performance.

Various factors influence these characteristics, including the type of plasticizer and its proportion in the plastisol, the particle size of the polymer and the presence or absence of other optional ingredients, especially fillers, viscosity modifiers and volatile diluents, the nature of such optional additional ingredients being generally known in the art. Preferred plastisols for use in the present invention contain, per 100 parts by weight of the vinyl chloride polymer, from 50 to 100 parts by weight of plasticizer, up to 100 parts, preferably up to 20 parts, by weight of filler, and up to 10 parts by weight of volatile diluents. Foamable compositions will also contain blowing agents, usually in an amount up to 3 parts by weight per 100 parts by weight of vinyl chloride polyer, and stabilisers and kickers for functioning in conjunction with the blowing agent.

The invention is illustrated by the following Examples.

EXAMPLE I A plastisol having the following composition, typical of compositions used to give a transparent compact resin layer, was prepared by mixing the ingredients: Parts by weight PVC Emulsion grade ... 100 Modified benzyl phthalate plasticizer ... ... ... 52 BaCdZn stabilizer 2 A coating of this formulation was applied, using a system as illustrated in the drawings, to a gelled foamable vinyl layer previously coated on to an asbestos paper base. For the application of the above formulation, the cylindrical screen had an external diameter of 640 mm. a thickness of 0.25 mm, and hexagonal apertures such that the distance (a) in Figure 1 was 1.8 mm and the distance (b) was 1.0 mm.The angle of contact of the flexible blade 6 with the interior wall of the screen was set at 60 , the linear speed of the substrate (printing speed) was set at 10 metres/min., and plastisol was fed to the interior of the cylinder at a rate sufficient to maintain a stable bank of plastisol 9.

Under these conditions the layer of plastisol deposited on the substrate had a thickness of 0.4 mm corresponding to a weight of plastisol of 500 gm/m2.

EXAMPLE 2 A plastisol having the following composition, typical of compositions used to give a foamable plastisol layer, was prepared by mixing the ingredients: Parts by 'weight PVC.Emulsion grade ., 100 Modified benzyl phthalate plasticizer ... ... ... 55 Blowing agent ... ... ... 2 Kicker ... ... ... ... 2 Titanium dioxide 5 Pigment ... ... ... ... 1 A coating of this formulation was applied to a substrate sheet of vinyl-coated cloth using a system as illustrated in the drawings wherein the cylindrical screen had an external diameter of 640 mm, a thickness of 0.25 mm and hexagonal apertures such that the distance (a) in Figure 1 was 2.0 mm and the distance (b) was 1.1 mm.The coating speed was 15 m/min, the flexible blade 6 was set to contact the inner wall of the screen at an angle of 45 , and plastisol was fed to the interior of the cylindrical screen at a rate sufficient to maintain a stable bank of plastisol 9. Under these conditions the layer of plastisol deposited on the substrate had a thickness of 0.65 mm corresponding to a weight of plastisol of 850 grams/metre2.

WHAT WE CLAIM IS: 1. A process for the application to a substrate of a continuous coating of a plastisol of a vinyl chloride polymer, which comprises supplying the plastisol to the interior of a rotating cylindrical metal screen having a substantially uniform distribution of apertures, the outer surface of the screen being in contact with a continuously moving sheet of substrate, and the interior of the screen having located therein constriction or scraper means such that the plastisol is forced through the apertures of the screen and on to the substrate, the screen having a thickness of at least 0.20mm, the total area of the apertures being at least 25% of the total area of the screen, and the rates of supplying the plastisol to the cylinder, passage of the plastisol through the apertures and rotation of the cylinder being such that the coating of plastisol formed on the substrate by coalescence of the individual initially applied spots of plastisol has a thickness of from 0.35 to 1.0 mm.

2. A process according to Claim 1, in which the apertures in the screen are poly

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. weight of the copolymer is derived from the vinyl chloride. Suitable plasticizers for use in preparing the plastisols include phthalates, for example alkyl benzyl phthalates such as butyl benzyl and octyl benzyl phthalate, and blends of phthaiates with modifiers. Also suitable are alkyl diaryl phosphates. The plastisol used in the process of the invention is formulated to have suitable viscosity and other rheological characteristics and good, gelation performance. Various factors influence these characteristics, including the type of plasticizer and its proportion in the plastisol, the particle size of the polymer and the presence or absence of other optional ingredients, especially fillers, viscosity modifiers and volatile diluents, the nature of such optional additional ingredients being generally known in the art. Preferred plastisols for use in the present invention contain, per 100 parts by weight of the vinyl chloride polymer, from 50 to 100 parts by weight of plasticizer, up to 100 parts, preferably up to 20 parts, by weight of filler, and up to 10 parts by weight of volatile diluents. Foamable compositions will also contain blowing agents, usually in an amount up to 3 parts by weight per 100 parts by weight of vinyl chloride polyer, and stabilisers and kickers for functioning in conjunction with the blowing agent. The invention is illustrated by the following Examples. EXAMPLE I A plastisol having the following composition, typical of compositions used to give a transparent compact resin layer, was prepared by mixing the ingredients: Parts by weight PVC Emulsion grade ... 100 Modified benzyl phthalate plasticizer ... ... ... 52 BaCdZn stabilizer 2 A coating of this formulation was applied, using a system as illustrated in the drawings, to a gelled foamable vinyl layer previously coated on to an asbestos paper base. For the application of the above formulation, the cylindrical screen had an external diameter of 640 mm. a thickness of 0.25 mm, and hexagonal apertures such that the distance (a) in Figure 1 was 1.8 mm and the distance (b) was 1.0 mm.The angle of contact of the flexible blade 6 with the interior wall of the screen was set at 60 , the linear speed of the substrate (printing speed) was set at 10 metres/min., and plastisol was fed to the interior of the cylinder at a rate sufficient to maintain a stable bank of plastisol 9. Under these conditions the layer of plastisol deposited on the substrate had a thickness of 0.4 mm corresponding to a weight of plastisol of 500 gm/m2. EXAMPLE 2 A plastisol having the following composition, typical of compositions used to give a foamable plastisol layer, was prepared by mixing the ingredients: Parts by 'weight PVC.Emulsion grade ., 100 Modified benzyl phthalate plasticizer ... ... ... 55 Blowing agent ... ... ... 2 Kicker ... ... ... ... 2 Titanium dioxide 5 Pigment ... ... ... ... 1 A coating of this formulation was applied to a substrate sheet of vinyl-coated cloth using a system as illustrated in the drawings wherein the cylindrical screen had an external diameter of 640 mm, a thickness of 0.25 mm and hexagonal apertures such that the distance (a) in Figure 1 was 2.0 mm and the distance (b) was 1.1 mm.The coating speed was 15 m/min, the flexible blade 6 was set to contact the inner wall of the screen at an angle of 45 , and plastisol was fed to the interior of the cylindrical screen at a rate sufficient to maintain a stable bank of plastisol 9. Under these conditions the layer of plastisol deposited on the substrate had a thickness of 0.65 mm corresponding to a weight of plastisol of 850 grams/metre2. WHAT WE CLAIM IS:

1. A process for the application to a substrate of a continuous coating of a plastisol of a vinyl chloride polymer, which comprises supplying the plastisol to the interior of a rotating cylindrical metal screen having a substantially uniform distribution of apertures, the outer surface of the screen being in contact with a continuously moving sheet of substrate, and the interior of the screen having located therein constriction or scraper means such that the plastisol is forced through the apertures of the screen and on to the substrate, the screen having a thickness of at least 0.20mm, the total area of the apertures being at least 25% of the total area of the screen, and the rates of supplying the plastisol to the cylinder, passage of the plastisol through the apertures and rotation of the cylinder being such that the coating of plastisol formed on the substrate by coalescence of the individual initially applied spots of plastisol has a thickness of from 0.35 to 1.0 mm.

gons of uniform size and shape located at regular intervals in rows and such that adjacent edges of adjacent apertures are parallel and such that on a median line drawn through a row of apertures, the distance separating the adjacent parallel edges of two adjacent apertures is not greater than the distance across an aperture.

3. A process according to Claim 2, in which the distance across an aperture is from 1.0 to 2.0 mm.

4. A process according to any of Claims 1 to 3, in which the total area of the apertures is from 35 to 75% of the total area of the screen.

5. A process according to Claims 1 to 4, in which the plastisol contains, per 100 parts by weight of the vinyl chloride polymer, from 50 to 100 parts by weight of plasticizer.

6. A process according to Claim 5, in which the plastisol contains up to 100 parts by weight of a filler per 100 parts by weight of the vinyl chloride polymer.

7. A process according to either of Claims 5 and 6, in which the plastisol contains up to 10 parts by weight of a volatile diluent per 100 parts by weight of vinyl chloride polymer.

8. A process according to Claim 1 substantially as described with reference to the 'drawings.

9. A process for the production of a composite comprising a plasticized vinyl chloride polymer layer on a substrate, which comprises heating a plastisol-coated substrate that has been obtained by a process according to any of Claims 1 to 8 to gel and cure the plastisol.

10. A composite that has been obtained by a process according to Claim 9.