GB1602120A - Process for applying a patterned coating to substrates - Google Patents

Description

(54) A PROCESS FOR APPLYING A PATTERNED COATING TO SUBSTRATES (71) We, GORDON ELLIS & COMPANY, a British Body Corporate, of unlimited liability of Trent Lane, Castle Donington, Near Derby, 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:- The present invention concerns a process for applying a patterned finish to substrates and substrates when produced by said process.

The invention relates especially but not exclusively to a process for applying a wear and stain-resistant coating to hardboard or chipboard, but is equally applicable to other coatings for other substrates, for example substrates of wood or wood substitutes, minerals such as asbestcs or ceramics materials or glass.

In the past, when it was desired to coat, for example a sheet of hardboard to provide a patterned table mat or tray top an adhesive coat was first applied to the hardboard, after which a sheet of paper carrying the pattern and covered by an acetate film was applied to the hardboard.

A further, but more expensive method, was to cover the hardboard with a first layer of melamine material, apply a thin paper of a suitable type and carrying the printed pattern to the base melamine layer and thereafter cover the printed paper pattern with at least one other melamine layer. The assembly was then heated under pressure to combined the layers to provide a laminate and to cure the melamine.

Sheets coated by the first method described above, while being relatively inexpensive, have not been scratch and wear resistant for a prolonged period of time. Sheets coated by the second method have been more scratch and wear resistant than those of the first method but their manufacture has been time consuming and expensive.

It is an object of the present invention to obviate or mitigate the above disadvantages.

Hereinafter in this specification the term paper transfer print" will be utilised. This term is intended to define a backing member with a pattern printed thereon, the intention being that the backing member carries the pattern only temporarily between the printing process which applies the pattern to the member and the application of the pattern to another article, during which application the backing member is separated from the printing medium. The term is used to cover printed transfer prints including any suitable flexible backing member, for example, paper, and any printing medium applied thereto to provide a pattern by any suitable means, for example, off-set printing and screen printing.

According to the present invention there is provided a process for applying a patterned finish to a substrate comprising applying a coating of acrylic resin or modified acrylic resin to the substrate, positioning a paper transfer print on the coating and transferring the printed pattern from the transfer print to the coating.

Some embodiments of the present invention will now be described by way of example only.

EXAMPLE A A sheet of hardboard was pretreated by coating its underside to prevent the final product warping. The thus treated sheet was then cleaned by brushing to remove all dust particles therefrom and was passed through a curtain coating apparatus in which a thin film of coating medium was caused to fall vertically through a plane which is transvRrse to the longitudinal direction of movement of the sheet of hardboard through the apparatus. The thus coated hardboard sheet was then allowed to partially "dry" under atmospheric conditions and was thereafter passed through an oven in which any volatile material not removed from the coating during the atmospheric drying stage was removed prior to a chemical curing of the coating in a hotter region of the oven.

Conveniently the first coating applied to the hardboard sheet is white in colour and is a modified acrylic resin mixed with a reactor and thinners to the required viscosity.

Conditions in the coating apparatus are adjusted such that a coating weight of 10 to 15 grammes per square foot is achieved and the curing is carried out at at least 80"C for 10 to 15 minutes.

After the material coated with the first white coat of acrylics material has cured, a second clear coat is applied in a similar manner and similarly cured.

The pattern can then be applied to the coated hardboard sheet by placing a paper transfer print thereon and subjecting the sheet and print to heat and pressure in a plate press.

So that an efficient transferance of dye from the printing medium to the coating can be achieved it is necessary to ensure that the transfer print and the top surface of the sheet are in intimate contact, and that they are heated to a sufficient temperature and for sufficient time to allow the transfer or sublimation process to take place.

To achieve intimate contact the plates of the press, especially the plate adjacent the transfer print is covered by a blanket of a compressible, heat resistant, heat conductive material. To achieve the correct temperatures and transfer times the press has appropriate thermostatic controls and timing devices.

Further to obviate or mitigate any tendency of the substrate to warp, heat is applied to both sides thereof in the press.

The substrate may be sheet, or may be a component of an article of furniture.

for example a cot end, bed end, or kitchen cabinet door. With such components engineered patterns may be applied thereto by providing a transfer print having the same dimensions as the component. The transfer may simultaneously provide a border pattern and a central patterned area.

After treatment in the heated press the backing member of the print is removed from the sheet, the coating of which permanently carries the printed pattern.

The section of coating material and printing medium is important to the success of the present invention.

For example the coating should be sufficiently receptive to admit the dye from the printing medium but at the same time should not be so receptive that the dye permeates into regions of the coating where no dye is required, otherwise a smudged, discoloured pattern may result. It must be compatible with the dye such that it does not effect, for example the dye colouring, it must not adhere to the paper of the transfer print, especially when they are heated during the transfer operation and it must, when coloured, retain its colour during and after the transfer process and in subsequent prolonged use. It must also be cureable at temperatures which are readily achieved and have a curing time which is not excessive. Further it must be capable of being worked, for example sawn or drilled without any adverse effects but at the same time provide a durable surface.

Similarly the dye must be carefully chosen to be suitable for the process and to be compatible with the lacquer, and if different dyes are used together, they must be matched such that they sublime at the same temperature. This means in effect that they must reside in the same molecular weight band.

With the particular lacquers selected, transfer of dye thereto may be achieved at temperatures as low as 1500C, that is below the temperature at which the dyes sublime. To obtain efficient transference at these temperatures, however, perfect, total intimate contact is required. Thus a process utilising temperatures above the sublimation temperature, that is 1800C (up to 2500 C) is preferable as total intimate contact is not thus totally essential.

The dyes may be incorporated in a printing medium which is suitable for screen printing or for litho printing.

As outlined above the process involves the use of dyestuffs that transfer with the assistance of heat and pressure into a resinous surface consisting of a convertible coating of an acrylic resin or a modified acrylic resin alone or in combination with amino resin or an isocyanate terminated prepolymer or combinations thereof. Using these resinous materials in a converted state on nonmetallic substrates dyestuffs can be used at elevated temperatures to produce engineered or multicolour designs suitable for decorative or functional purposes.

Any non-metallic heat stable substrate may be prepared to accept the transfer print by applying a surface coating consisting of a synthetic resinous convertible coating based cn acrylic, a modified acrylic or an acrylated alkyd resins or an acrylic modified polyester resin alone or in combination with an amino or an isocyanate terminated prepolymer or both. Suitable coating systems include solutions of hydroxyl terminated acrylic resins in combination with isocyanate prepolymers, hydroxyl terminated acrylic resins in combination with melamine formaldehyde resins with or without an acid catalyst such as para toluene sulphonic acid, hydrochloric acid, phosphoric acid or sulphuric acid, acrylated alkyd resins in combination with amino resins such as melamine formaldehyde or urear formaldehyde resins, and acrylic resins based on acrylamide.

The coatings can be applied both pigmented or clear or both at the required thickness by any suitable conventional methods such as curtain coating as described in Example A, of roller coating or spraying before curing in a suitable oven heated by hot air or infra red or in certain cases may be cured at ambient temperatures.

Examples of suitable coated substrate systems for transfer printing include the following: EXAMPLE B Acid cured thermosetting hydroxyl terminated acrylic resin together with a urea formaldehyde or melamine formaldehyde resin co-reactant. This is a two coat system for application for example onto hardboard and is cured for example by hot air. Other fibre based boards, resin impregnated fibre board or carton board or even paper board may be suitably coated.

The base coat consists essentially of a solution of hydroxyl terminated acrylic resin or resins together with solvents such as aromatic hydrocarbons, medium boiling alcohols and oxygenated solvents such as medium-low boiling ketones or aliphatic esters or a blend of these solvents. Pigments such as titanium dioxide, zinc oxide or in special cases heat resistant inorganic pigments such as yellow oxide, brown umber, red oxide etc., or any blend together with mineral fillers such as talc or china clay are blended into the resin by ball milling or sand milling or other suitable process. The pigment dispersion is made into a paint by addition of further resin, other resins such as urea formaldehyde or melamine formaldehyde or even hexa-methoxy methyl melamine together with such solvents as are necessary for ease of application.

Acid catalysts which may be para toluene sulphonic acid or sulphuric or hydrochloric or phosphoric acid or any combination are added as a convenient solution at the time of use.

A typical formulation has the ratio acrylic resin to melamine formaldehyde resin of from 3.5 to 1 to 5 to 1 on a solids:solids basis and uses from 1 to 5 percent of free acid again on a solids:solids basis; the whole being stoichiometrically calculated beforehand. All components are carried in suitable solvents as specified above and the various ratios are adjustable to suit the dry film characteristics required and the stoving/curing facilities available.

The top coat is of essence very similar save that pigment and extenders are omitted. The finish may be gloss or matt depending on level of matting agent incorporated -- such matting agents being for example finely dispersed silicaceous materials. For various process reasons additions may be made of suitable solutions of flow control or levelling agents or solutions of waxes for surface slip and mar resistance if required in that particular application.

The base coat is conventionally applied by spray or roller coater or curtain coater to give a wet film of 2-20 g/sq. ft. dry film thickness 0.5-5.0 thousandths of an inch (12.5-125 microns) and may be air dried or cured under a flow of hot air at temperatures up to 1200C. A typical installation uses a hot air circulating oven of proprietary design with a dwell time of 10 minutes at 900C in the hottest part of the oven.

After cooling and sanding or denibbing for optimum adhesion the top coat may be applied and stoved in a similar manner whereafter the board is suitable for immediate transfer printing as described elsewhere or may be conventionally cooled, stacked and stored for printing at a later date.

EXAMPLE C In another example an aliphatic or aromatic or mixed nature isocyanate prepolymer is mixed together with a thermosetting hydroxyl terminated acrylic resin. This lacquer system may be applied as a clear two pack one coat finish onto paper laminated chipboard or impregnated paper laminated chipboard of proprietary grade.

The lacquer consists of a solution of a hydroxy terminated acrylic resin for example of hydroxyl equivalent weight 600. The lacquer may be modified for gloss or mattness by incorporation of a silicaceous matting agent where necessary and other process aids such as levelling or flow agents, dispersion acids or waxes may be added. If required it is possible to add small quantities of optical brighteners or transparent dyes.

At the time of use the lacquer is mixed with a stoichiometrically calculated quantity of isocyanate prepolymer of essentially aromatic nature together with such solvent as may be necessary to achieve coating viscosity. Coatings may be applied as previously detailed. Alternatively an aliphatic isocyanate or blended isocyanate prepolymer may be used to give enhanced light fastness and heat resistance to the coating.

Typically the lacquer is applied at a viscosity of 30--90 seconds B4 flow cup at 25"C in a curtain coater at between 4--20 g per sq. ft. (dry film thickness 1--5 thou, 25-125 microns) with a typical drying schedule of e-5 minutes solvent flash off followed by 0--5 minutes in a warm air circulating unit followed by 30-120 seconds under infrared radiant heating in an oven unit of proprietary construction.

The board is then ready for transfer printing or may be cooled to ambient temperature and stacked for printing on a more convenient occasion.

Such proprietary boards suitable for this treatment include Ecopan from Mervyn Young of Weybridge those from Pellos Products and certain Catalin (Registered Trade Mark) paper faced chipboards. Lower quality grades of chipboard and even low quality boards such as flaxboard or even cork based substrates suitably sealed may be coated and may need a primer coat prior to the top coat. Such primers are usually based on the resins described above and incorporate titanium dioxide pigment or other inorganic heat resistant pigments together with extenders as described previously.

EXAMPLE D In a further example float glass of 3-5 millimetres thickness has been coated and transfer printed using a lacquer based on certain acrylamide modified acrylic resins. Optimum film properties may be developed by judicious additions for example of 0--20 on a solids basis of a low molecular weight Bisphenol A type diepoxide which may itself be modified with a diglycidyl ether or other low molecular weight prepolymer.

Alternatively ceramic tiles or even sealed grades of asbestos or asbestos board substitutes may be similarly coated for transfer printing with an acrylated alkyd resin system together with a stoichiometrically calculated amount of melamine formaldehyde resin or even hexamethoxymethyl melamine typically in the ratio of 3 to 1 to 5 to 1 but more usually 4 to 1 on a solids: solids basis with the acrylated alkyd component in preponderance.

A typical application has the resin component or components dispersed in medium-high boiling aromatic or mixed nature solvents together with medium boiling aliphatic alcohol or ester solvents. Suitable flow control or levelling agents may be added to give a gloss one pack coating that may be matted if required with silicaceous materials. Other process aids may be incorporated as required.

Application is usually by automatic or hand spray or by curtain coater to give a wet film thickness of 3-15 g/sq. ft. dry film thickness 0.4--2.0 thousandths of an inch (l(w50 microns). The stoving schedule is an optimum 30 minutes at 150- 200"C while the flash off period is controlled by the film weight applied.

The printing medium includes a dye or dyes and a carrier medium, the medium depending to a certain extent upon the printing technique to be employed. The dyes used sublime readily at and above temperatures of 1800C and penetrate into the coating by diffusion. They are disperse dyes surfactant treated to maintain submicron particle size. Examples of typical dyes are: C.I. disperse yellow 54 (C.I.=Colour Index).

C.I. disperse red 4 and 11.

C.I. disperse blue 3 or 14.

The paper to which the printing medium is applied is of suitable smoothness for printing and contains no additives which have an affinity to the dyes used.

Machine finished paper of 75 g.s.m. is suitable.

A suitable formulation for the printing medium for a lithographic process is given below: Component Amount Examples

Dye 1 to a total Pigment extender I pigment content Alumina, of 2530% by calcium weight carbonate, light magnesium carbonate.

Dispersing vehicle 2025% by Drying oil; weight linseed modified penta erythritol esterified alkyd resin Pigment wetting approx. 10% medium by weight Printability medium 30% by Dispersion of to promote lithographic weight a Maleic resin, properties high melt point low acid.

Metallic dryers balance An equivalent printing medium for a screen-printing process includes, dyes, pigment extenders and dispersing vehicle as above, and resin, solvent and thickener.

An example of a lithographic printing medium is now set out:- EXAMPLE E Print a one colour design on an offset lithographic printing machine Paper Sheets of 75 g.s.m. machine finished bleached sulphite paper.

Ink 15% by weight blue dye L. B. Holliday Sublaprint 70032.

10% by weight pigment extender Hakuenka O.T. from Croton Garry Ltd.

25% by weight dispersing mediun Ennelkyd (Registered Trade Mark) 604 from Leon Frenkel Ltd.

15% by weight pigment wetting medium 50 Poise Linseed Stand Oil.

30% by weight printability medium Halex (Registered Trade Mark) varnish from Lawter Chemicals Ltd.

0.4% by weight lead drier (18% metal).

4.5% by weight 280/3 100C petroleum distillate 0.1% by weight 6% cobalt drier.

Various modifications can be made without departing from the scope of the invention, for example the coating may be applied by roller coating or spraying.

Further the transfer operation may be achieved in some apparatus other than a plate press, for example a roller press, or a diaphragm press.

WHAT WE CLAIM IS: 1. A process for applying a patterned finish to a substrate comprising applying a coating of acrylic resin or modified acrylic resin to the substrate, positioning a paper transfer print on the coating and transfering the printed pattern from the transfer print to the coating.

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

Claims (29)

**WARNING** start of CLMS field may overlap end of DESC **. The paper to which the printing medium is applied is of suitable smoothness for printing and contains no additives which have an affinity to the dyes used. Machine finished paper of 75 g.s.m. is suitable. A suitable formulation for the printing medium for a lithographic process is given below: Component Amount Examples Dye 1 to a total Pigment extender I pigment content Alumina, of 2530% by calcium weight carbonate, light magnesium carbonate. Dispersing vehicle 2025% by Drying oil; weight linseed modified penta erythritol esterified alkyd resin Pigment wetting approx. 10% medium by weight Printability medium 30% by Dispersion of to promote lithographic weight a Maleic resin, properties high melt point low acid. Metallic dryers balance An equivalent printing medium for a screen-printing process includes, dyes, pigment extenders and dispersing vehicle as above, and resin, solvent and thickener. An example of a lithographic printing medium is now set out:- EXAMPLE E Print a one colour design on an offset lithographic printing machine Paper Sheets of 75 g.s.m. machine finished bleached sulphite paper. Ink 15% by weight blue dye L. B. Holliday Sublaprint 70032. 10% by weight pigment extender Hakuenka O.T. from Croton Garry Ltd. 25% by weight dispersing mediun Ennelkyd (Registered Trade Mark) 604 from Leon Frenkel Ltd. 15% by weight pigment wetting medium 50 Poise Linseed Stand Oil. 30% by weight printability medium Halex (Registered Trade Mark) varnish from Lawter Chemicals Ltd. 0.4% by weight lead drier (18% metal). 4.5% by weight 280/3 100C petroleum distillate 0.1% by weight 6% cobalt drier. Various modifications can be made without departing from the scope of the invention, for example the coating may be applied by roller coating or spraying. Further the transfer operation may be achieved in some apparatus other than a plate press, for example a roller press, or a diaphragm press. WHAT WE CLAIM IS:

1. A process for applying a patterned finish to a substrate comprising applying a coating of acrylic resin or modified acrylic resin to the substrate, positioning a paper transfer print on the coating and transfering the printed pattern from the transfer print to the coating.

2. A process as claimed in Claim 1, in which the coating comprises at least two

layers.

3. A process as claimed in Claim 2, in which the layers are applied by a curtain coating technique.

4. A process as claimed in Claim 2, in which the layers are applied by roller coating technique.

5. A process as claimed in Claim 2, in which the layers are applied by spraying.

6. A process as claimed in any one of the preceding claims, in which the coating includes an acrylic modified alkyd resin or an acrylic modified polyester resin.

7. A process as claimed in Claim 6 in which said coating includes said resin and amino resin.

8. A process as claimed in Claim 6, in which said coating includes said resin and isocyanate terminated prepolymers.

9. A process as claimed in Claim 6, in which said coating includes said resin, amino resin and isocyanate terminated prepolymers.

10. A process as claimed in any one of the preceding claims in which said coating is pigmented.

11. A process as claimed in any one of the preceding claims in which said coating is clear.

12. A process as claimed in any one of the preceding claims in which the coating is cured by heating.

13. A process as claimed in any one of the preceding claims in which the coating is cured at ambient temperature.

14. A process as claimed in any one of the preceding claims, in which the transfer print comprises a paper backing member and a pattern of printing medium thereon, said medium including a dye and a carrier, the dye being capable of solid/solid diffusion into the coating when heated.

15. A process as claimed in any one of the preceding claims, in which the transfer print comprises a paper backing member and a pattern of printing medium thereon, said medium including a dye, and a carrier, the dye being capable of sublimination-condensation diffusion into the coating.

16. A process as claimed in Claim 14 or Claim 15, in which the dye is a disperse dye surfactant treated to maintain sub-micron particle size during processing.

17. A process as claimed in Claim 14 or 15 or 16, in which the paper is suitably smooth for printing and contains no additives which have an affinity to the dye of the printing medium thereon.

18. A process as claimed in any one of Claims 14 to 17, in which the carrier includes a pigment extender, a dispersing vehicle, a pigment wetting medium, a printability medium and metallic dryers whereby it is applicable to the paper by a litho printing technique.

19. A process as claimed in any one of Claims 14 to 17, in which the carrier includes a pigment extender, a dispensing vehicle, a resin a solvent and a thickener whereby it is applicable to the paper by a screen printing technique.

20. A process as claimed in any one of the preceding claims in which heat and pressure are applied to the substrate, coating and transfer to effect the transfer of the printed pattern.

21. A process as claimed in Claim 20, in which heat is applied to both sides of the substrate.

22. A process as claimed in Claim 20 or Claim 21, in which a compressible heat conductive, heat resistant blanket is applied to the transfer on the substrate during the transfer operation.

23. A process as claimed in any one of the preceding claims in which the paper transfer has dimensions corresponding with the dimensions of the substrate.

24. A process substantially as hereinbefore described with reference to Example A.

25. A substrate when coated by a process as claimed in any one of the preceding claims.

26. A process as claimed in any one of Claims 1 to 24, in which the coating comprises the composition described herein in Example B.

27. A process as claimed in any one of Claims 1 to 24, in which the coating comprises the composition described herein in Example C.

28. A process as claimed in any one of Claims 1 to 24, in which the coating comprises the composition described herein in Example D.

29. A process as claimed in any one of Claims 1 to 24 or 26 to 29 in which the paper transfer print comprises the composition described herein with reference to Example E.