GB1559655A - Release sheet and coating compositions therefor - Google Patents

Description

(54) RELEASE SHEET AND COATING COMPOSITIONS THEREFOR (71) We, FORMICA CORPORATION, a company organised and existing under the laws of the state of Delaware, United States of America, of 120 East Fourth Street, Cincinnati, State of Ohio, United States of America, 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 is in the field of high and low pressure decorative laminates, and relates to a release sheet for use in the manufacture of such laminates, and to com positions useful in the making of such release sheets.

Presently known art in the manufacture of textured high pressure decorative laminates inclues the following process : An assembly consisting of the following is placed in a flat-bed hydraulic press, whereupon heat and pressure are applied: Iron Paper cushion Stainless steel plate Laminated aluminum-paper caul stock Overlay sheet Decor sheet Layers of phenolic-kraft core stock Separator sheet (center line) The assembly is symmetrical about the center line and therefore only the upper half is shown.

The aluminum-paper caul stock now commonly used consists of alloy No. 1, 100, usually in fully annealed state (-0 temper), but also frequently in a harder state such as H-18 or H-19 (full hard). The aluminum foil portion may have a matte finish, a polished finish or a mill finish on its exposed face. Typically, the aluminum is bonded to a paper of about 40 Ibs./ream by means of casein adhesives.

When fully annealed alloy No. 1100 in a thickness of. 0005 inches is laminated matte side to a 40 Ib./ream machine glazed natural kraft paper, it is often called "No. 6 Caul Stock". When used in the above assembly, it will produce a high pressure laminated with a suede finish. Its gloss usually will be from S10 measured on a Gardner 60 glossmeter, and will depend upon the particular specimen of caul stock chosen. Most rolls will produce laminates of about 6-8 gloss, but others will produce values up to 10 or higher.

Because of this variation in gloss, it is customary to finish these laminates by the process of"dull rubbing". In this process the laminate is passed through a machine in which its decorative surface is contacted by a number of rotating, cylindrical, nylon fiber brushes. The brushes are flooded with a slurry of pumice and water which abrades the laminate surface and reduces its gloss by about from 15 depending upon the force which is used to bring the brush into contact with its surface. Typically, a laminate emerging from the press with a gloss of 6.5 would be dull rubbed with light contact pressure and abraded to a gloss of about 5. 5. A laminate having a gloss of 10, however, would require a substantially higher force to bring the brush into very firm contact with the laminate. Even then the reduction in gloss might be only about 3 , say to about 7 .

If the aluminum foil caul stock were, more uniform, it would produce laminates having glosses within the range of 62, which is commercially desirable. The dull rubbing could then be eliminated which would reduce the cost of manufacture. Additionally, the micro-scratches imparted to the laminated surface during dull rubbing render it less resistant to staining, due to the fact that thousands of microcracks are introduced into the surface into which very small particles of staining or soiling materials may enter and lodge tenaciously.

The suede texture has proven to be of special importance because it is attractive to the touch, yet serves to overcome"telegraphing"of joints, glue lines, coarse grain and other discontinuities which may occur in modem furniture structures, especially those which use frame construction as opposed to solid panels, e. g. in a table top.

"Telegraphing"is used in the industry to designate the ability of a sheet to reproduce in its upper surface whatever texture may be possessed by the substrate upon which it rests. Thus, for many years, the best practice in mounting high pressure laminates was to use hardwood faced plywood, usually birch or maple. With the advent of reconstructed wood particleboard for laminate substrates, it became the practice to use three layer construction which featured a layer of"fines"on the bondable surfaces to eliminate"telegraphing".

Fourniture manufacturers learned that the suede surface is only mildly textured and that the ultimate furniture user will not be unduly aware of the depth of the texture. For instance, such a textured laminate will provide a suitable writing surface if used as a desk top.

Because of this unique dimension in texture, i. e. one which is coarse enough to hide telegraphing, yet smooth enough to be accepted as planar, this"mini texture" has enjoyed great popularity and now accounts for over 50% of all the commercial laminates produced in the U. S.

The amount of aluminum foil used in laminate production is very substantial so that the aggregate value of such foil consumed annually is very great. Laminate manufacturers have, therefore, sought materials which would be lower in cost on a unit basis, since the annual savings to be realized are of an important magnitude.

One manner in which this may be accomplished is to replace the aluminum caul stock with a sheet of paper which is coated with a material which will fill surface voids and impart a texture of sufficient smoothness and gloss to the surface of a decorative laminate. Textured laminates may have useful gloss levels ranging from about 6 units to about 25-30 units.

It is necessary for the texturing sheet to release readily after it has been used on the laminate, hence a release agent of some type is often applied in a very thin layer over the basic texturing coat. In U. S. Patent No. 3,946,135 to Peterson, such a release paper is described. Said release paper comprises a first coat constituting a clay-adhesive base coat and a second coat of a thermosetting resin.

Single coat release sheets can be prepared by the use of an additive in the texturing coat which makes it releasable upon drying. Such a material is called an "internal release agent"because it is contained internally in the texturing coat as it is applied. Release agents which are applied as a distinctly second coat are called "external release agents"since they never enter the central volume of the texturing coat.

The present invention provides novel release compositions which can be used te produce release sheets used in the production of laminates via heat and pressure consolidation of resin-impregnated paper sheets, and also release sheets per se. In preferred embodiments, the present release compositions provide the release sheets with the type of surface required of commercial users at a much lower cost than aluminum foil release sheets.

The novel release compositions of the present invention comprise an organic solvent solution containing from 0.5% to 80%, by weight, based on the total weight of the composition, of an organic solvent soluble mixture comprising 1) from 73% to 99%, by weight, based on the total weight of (1) and (3), of an oil-modified alkyd resin, 2) from 30% to 70%, by weight, based on the total weight of (1) of a poly- alkylether of a polymethylol melamine, and 3) from 1% to 25%, by weight, based on the total weight of (1) and (3), of a copolymer containing from 15 to 85 mole percent of recurring units having the formula

wherein each R is, individually, OR', RI being hydrogen or Cl-C22 alkyl, or the two R groups taken together form an oxa group and the remaining units are recurring units of the formula

wherein R'is hydrogen or methyl, R'is a CgZso alkyl radical and X is 0 or CH2.

The novel texture-release sheets of the present invention comprise either a single coated paper sheet or a paper sheet coated with a double release layer. The single coating texture-release sheet comprises 1) a cellulosic paper sheet coated with a composition comprising A) from 75% to 99%, by weight, based on the total weight of (A) and (B), of an oil-modified alkyd resin which is cross-linked with from 30% to 70%, by weight, based on the total weight of (A) of a polyalkylether of a polymethylol melamine, and B) from 1% to 25%, by weight, based on the total weight of (A) and (B), of a copolymer containing from 15 to 85 mole percent of recurring units having the formula

wherein each R is as defined above, and the remaining units are recurring units of the formula

wherein R2, R3 and X are also as defined above.

The novel double layered texture-release sheet of the present invention comprises 1) a cellulosic paper sheet coated with a first coating (A) comprising an oilmodified alkyd resin which is cross-linked with from 30% to 70%, by weight, based on the total weight of the alkyd of a polyalkylether of a polymethylol melamine, and a second coating (B), atop said (A), comprising a copolymer containing from 15 to 85 mole percent of recurring units having the formula

wherein each R is as defined above, and the remaining units are recurring units of the formula

wherein R2, R'and X are also as defined above.

The substrates utilized to form the novel release sheets of the present invention comprise any cellulosic sheet such as bleach sulfate, kraft, clay coated kraft, parchment, clay coated parchment, greaseproof paper, glassine and paper clay coated publication paper. Greaseproof paper is well known to those skilled in the art as is glassine paper, a complete description of each being set forth in the Second Edition, Volume III, of Papermaking and Paperboard Making, McGraw-Hill Book Company, 1969, page 182, Pulp and Paper Manufacture, Ronald G. MacDonald, Editor.

Suitable oil-modified alkyd resins for use herein are well known in the art, and are generally disclosed for example in U. S. Patent Nos. 2,579,980 ; 2,600,623 ; 2,618,617; 2, 648,642; 2,649,423.

In the preparation of the oil-modified alkyd resins useful herein, the amount of oil present as a modifier suitably ranges from 5% to 50%, by weight, based on the total weight of the modifie alkyd resin. The alkyd resins may be prepared from saturated or unsaturated polycarboxylic acids; however, the saturated acids are preferred. Suitable acids include phthalic, isophthalic, terephthalic, succinic, oxalic, malonic, succinic, glutaric, sebacic, adipic, pimelic, suberic, azelaic, citric, tricarballylic, tartaric, malic, maleic, fumaric and itaconic acids.

Suitable polyhydric alcools include ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, trimethylene glycol, pinacol, trimethylol propane, neopentyl glycol, arabinol, sorbitol, glycerol, and pentaerythritol.

Suitable reaction conditions already known in the art may be employed, a slight excess of the alcohol being used to ensure complete rection. Among the oils which may be used to modify the alkyd resin are tung oil, tall oil, perilla oil, linseed oil, hemp seed oil, castor oil, cottonseed oil, corn oil, olive oil, peanut oil, cod liver oil and candlenut oil.

The oil-modified alkyd resin of the compositions used to form the release compositions of the instant invention are cross-linked with a suitable polyalkylether of a polymethylol melamine Examples of these melamine materials encompass the dimethyl, diethyl, dipropyl, dibutyl etc. ethers; the trimethyl, triethyl, tripropyl, tributyl ethers; the tetramethyl, tetraethyl, tetrapropyl, tetrabutyl etc. ethers; the pentamethyl, penta ethyi, pentapropyl, pentabutyl etc. ethers; and the hexamethyl, hexaethyl, hexapropyl, hexabutyl etc. ethers of the dimethylol, trimethylol, tetramethylol, pentamethylol or hexamethylol melamines. Of course, mixed polyalkyl ethers such as the dimethyl, tetraethyl ethers of the polymethylol melamines may also be used. The preferred melamine material is hexakismethoxymethyl melamine, In preparing the polymethylol melamines, a preferred mole ratio of melamine to aldehyde, preferably paraldehyde, is 1: 3 to 1: 6, respectively, and the alcohol used to impart the a ! ky) ether portion to the melamine material is preferably a Cl-C, alcool. The amount of melamine material used to cross-link the oil-modified alkyd resin should range from 30% to 70% of the melamine material, based on the total weight of the oil-modified alkvd and the melamine material.

The vinyl ether or unsaturated alkyl copolymers which constitute the other component to the novel release compositions are also known to those skilled in the art, and are generally set forth in U. S. Patent No. 3,770,687, and their formation may be had via the method set forth therein and according to U. S. Patent No. 2,047,398.

The vinyl ether or unsaturated alkyl copolymer may be prepared by copolymer izing 15 to 85 mol percent of the vinyl ether or unsaturated alkyl monomer with correspondingly, 85 ro 15 mol percent of the maleic acid, ester or anhydride under conditions to produce copolvmers. The preferred comonomers are maleic anhydride and a Cls alkyl vinyl ether of octadecene-l The compositions of the instant invention for single coating are solutions of from 0.5% to 80.0%, by weight, based on the total weight of the composition, of the alkyd resin, melamine material and copolymer in an organic solvent and are applied to the substrates as such. Useful solvents include aromatic hydrocarbons such as benzene, toluene and xylene ; aliphatic hydrocarbons such as hexane and heptane ; dimethyl- formamide ; butyrolactone ; tetrahydrofuran; isopropanol; dimethylsulfoxide ; dioxane and mixtures thereof.

The compositions may be prepared by individually dissolving the oil-modified alkyd, the polyalkylether of the polymethylol melamine and the copolymer individually in their own solvents and then blending the resultant solutions to produce the composition or the components may be added to a single solvent in the proper concentrations to produce the compositions. When a double layer release sheet is produced, the alkyd and melamine solutions are blended together before they are coated onto the substrate and then the copolymer solution is applied as a second layer.

The individual coatings may be applied to the paper substrate by any convenient means such as by reverse roll, air knife, gravure cylinder etc. to a total thickness of e. g. 0.1 to 0. 3 mil (1.5-5.0 Ibs/300 fI2 ream dry). When two coatings are applied, the cross-linked alkyd coating should preferably comprise at least 75% of the total coating thickness.

It is preferred that an acid catalyst be added to the release coating composition before application of it to the substrate in order to assure that the melamine compound fully cross-links the oil-modified alkyd. From 1. 0% to 10. 0%, by weight, based on the total weight of the oil-modified alkyd and the melamine material of acid catalyst is generally used with p-toluene sulfonic acid being the preferred catalyst. Xylene sulfonic acid, o-and m-toluene sulfonic acids, ethyl acid phosphate, n-butyl phosphoric acid, phosphoric acid and hydrochloric acid are other acid catalysts which can be used.

When double coatings are employed, the acid catalyst should be added to the alkydmelamine coating.

If desired, such additives as conventional thickening agents and leveling agents, may be added to the coating composition in order e. g. to adjust its viscosity to the requirements of the coating equipment and to regulate pick-up.

The coated paper substrate is then subjected to curing which involves subjecting the release sheet to heat to cross-link the alkyd with the melamine compound. A temperature ranging from 200 F to 450 F is generally suitable, cross-linking generally being complete in from 5 minutes to 15 seconds, correspondingly. When double coat- ings are used, the cross-linking can be effected before or after application of the copolymer coating.

The release sheets produced from the compositions of this invention, as mentioned above, are useful in the production of decorative laminates in that as release sheets they are capable of withstanding the heat and pressure required to produce decorative laminates without deterioration and release completely and rapidly from the resinimpregnated surfaces of the laminates after they are removed from the laminating press. They may be used in the production of the so-called"high pressure"laminates wherein a series of 3-12 phenol/formaldehyde resin impregnated kraft sheets are utilized as a core medium upon which are superimposed a melamine resin impregnated decorative surface of some specific design i. e. simulated wood grain, and an overlay sheet which is also melamine resin impregnated, or so-called"low-pressure"laminates or panels which comprise a self-supporting substrate such as particleboard, plywood etc. upon which is heat and pressure consolidated a melamine resin impregnated decorative sheet, as described above. The amount of heat applied in the production of each type of product is about the same, i. e. from about 100250 F, however, the high-pressure laminates are produced ar a temperature of over 900 psi and usually 1'100-1500 psi while the low-pressure panels are produced below 900 psi, usually 250-750 psi.

The following examples are set forth for purposes of illustration.

All parts and percentages are by weight unless otherwise specified.

EXAMPLE A (COMPARATIVE) To 92. 5 parts of an alkyd resin solution produced from 39.7 parts of soya oil, 41.3 parts of isophthalic acid and 19.0 parts of glycerol and having a solids content of about 62%, a viscosity of 23-29 secs. 2 Zohn cup. 77.0 F and a density of 8.4-8.7 lbs,/gallon, in a 67/33 isopropanol/xylene solvent, and containing 30% of hexakismethoxymethyl melamine, are added 7.5 parts of a catalyst solution comprising 50% p-toluene sulfonic acid and 50 /O isopropanol. By means of a gravure printing cylinder having a quad cell pattern of diagonal count of 120 per inch and a cell depth of 0.0032" uniformly knurled over its entire face, the alkyd-catalyst mixture is applied to a 35 Ib./3000 ft. 2 ream bleached kraft grease-proof paper at a 0. 2 mil thickness. The coated paper is then cross-linked in a high velociry hot air oven for 30 secs. at 280 F. The coating weight, after cross-linking, is 3.5 Ibs./3000 ft. 4 ream.

In order to determine that the coating is cross-linked, two pieces of the coated paper are arrange so that the coated sides face each other. The assembly is placed in a quick acting press with a platen temperature of 450 F and maintained under 40 psi for 6 seconds. The paper sheets are removed, cooled to room temperature and then peeled apart by hand. The two sheets separate readily with no signs of sticking, picking of paper fibers or other evidence of undercure.

The coated paper is then cut into 4'X 8'sheets and placed in a press pack assembly as follows top to bottom: A. A stainless steel press plate with its polished surface facing downward.

B. A sheet of the coated paper with its coated surface downward.

C. A conventional overlay sheet comprising a 28 Ib./3000 ft 2 ream, a-cellulose paper having impregnated therein about 64 weight percent of a commercial melamine/formaldehyde laminating resin. The volatile content is about 5% D. A conventional pigmente decorative paper bearing a wood grain print, facing upward and having impregnated therein about 40 weight percent of a commercial laminating resin similar to that in the overlay. The volatile content is about 5"1,,.

E. Five plies of a 115 Ib./3000 ft. 2 ream kraft saturating paper having im pregnated therein 25 weight percent of a conventional phenol/formaldehyde laminating resin. The volatile content is again about 5%.

F. A layer of glassine paper as a separator sheet.

The entire assembly is then repeated in inverted order to produce a so-called "back-to-back"press assembly, whereupon it is fitted with conventional layers of cushion paper on the outside surfaces of the stainless steel press plates. The entire assembly is then sandwiched between appropriate cold rolled steel plates and placed into a conventional high presspre laminating press. A pressure of 1400 psi is applied to the assembly. It is heated to 142 C in about 25 minutes and held at that temperature for 12 minutes. The entire assembly is then cooled to room temperature and withdrawn from the press and the laminates are recovered.

It is found that the coated paper which was to act as a release sheet is bonded strongly to the decorative surface of the laminates and that only small pieces can be removed. Numerous white patches of paper fiber remain bonded even where pieces of the release sheet are removed.

EXAMPLE 1.

Following the procedure of Example A, the alkyd resin-melamine and catalyst solutions are combined to produce 100 parts of mixture. To the mixture are added 5. 0 parts of a 40% solution in toluene of an alkyl vinyl ether/maleic anhydride copolymer in which the alkyl vinyl ether mixture (96% Cls alkyl, 2% Cl6 alkyl and 2% C, o~, 4 alkyl vinyl ethers) is copolymerized with an equimolar amount of maleic anhydride.

The paper is then coated in the identical manner and used as a texturing-release sheet on a laminate as before.

It is found that the coated paper now releases readily from the laminate, leaving no particles of paper, resin or other debris. In order to measure the ease with which such paper can be stripped from the laminate, the following test is performed.

Using a sharp knife, a slit is made from the upper (uncoated) surface of the release sheet as it yet remains on the pressed laminate and before any effort has been made to disengage it from the laminate. The slit is cut along a straight fine using a metal rule as guide for a distance of ten inches. From one end of this slit, a second slit is cut for ten inches in a direction perDendicular to the first slit. At the point of intersection of these slits, a small flap is raised by the insertion of the knife edge and the paper is peeled from the laminate along a line bisecting the angle benveen the two slits; that is, along a line 45 to the original slits. When about 1.5 inches has been so lifted, a spring type paper clip is attached to the paper flap and the clip allowed to close so that it holds the paner firmly. A spring balance capable of reading up to 50 grams is attached to the paper clip and the stripping of the paper continued along the direction of the bisector. As the paper is stripped back, the line along which peeling occurs is anproximately perpendicular to the bisector and increases in length as peeling is continued. At the point where the paper-laminate contact line is 5 inches in length, the force required to continue peeling is noted on the balance. This is about 25 grams.

The test is repeated numerous times and forces from about 15 grams to about 40 grams along a 5 inch line of contact are noted. The numerical value of the force so measured is called the"cling strength" The laminate produced above is found to have a roughness (AA) of about 90 microinches and a'60 gloss of 5. 5.

EXAMPLES B-1 (COMPARATIVE) The following materials are added to the alkyd resin-melamine-catalyst solution of Example A in the amounts of 1 part, 5 parts and 10 parts.

B. Paraffin wax C. Stearic acid D. Oleic acid E. Sodium stearate F. Methyl stearate G. Petrolatum H. Polyethylene I. Lecithin J. Pentaerithrytol tetrastearate Each material in each of the said amounts is used in the resin-catalyst solution as a coating for the texturing paper. Each coated paper is then used as a release sheet during the production of a laminate.

None of the resultant sheets exhibit any releasing properties. The cling strength is in excess of 500 grams in all cases. In most cases, particles of paper stick to the laminate. In some cases, the paper cannot be removed from the laminate at all.

CLING STRENGTHS At a cling strength of 60 grams/5 in., it is found that the release paper can be stripped from the laminate without the picking of paper fiber or other residues. At much above this level, however, it is difficult to remove the entire sheet of release paper from the laminate surface. Commercial laminates are produced in volume in 5'X12'sizes. It is desirable that the person who is removing the release sheet for discard be able to do it with ease, usually with a gentle, sweeping pull from one end of the sheet. If the paper does not release easily from every part of the laminate, it is necessary to pull several times or even to walk around the sheet to loosen the more clinging areas. This takes time which means that either the conveyor line carrying the laminates to be stripped must be slowed or additional manpower is used. Either solution increases the cost of operation. Thus a maximum useful cling strength is below about 60 grams/5 in., with preferred values being in the range of 15--40 grams/5 in.

EXAMPLES K & L (COMPARATIVE) Commercial release agents known to be highly effective in causing release of melamine-formaldehyde materials from metal molds and of laminates from press plates are obtained. These are supplie in an aerosol can. The first (Example No. K) is stated to be a non-silicon so that later painting or spraying of the part will not be hindered. The second (Example No. L) also an aerosol, consists of telomers of fluoro- carbons.

Each of these compounds is recovered from the aerosol package by allowing the propellant to escape. That of Example No. K is added to an alkyd-melamine-catalyst solution of Example A in the amounts of 1,5 and 10 parts of the former to 100 parts of the latter.

In a similar manner, that of Example No. L is added at the level of 10 parts per hundred of alkyd-melamine-catalyst solution.

The alkyd containing the above additives are used to coat greaseproof papers and, in turn, the resultant coated papers are used as release sheets in high pressure laminate production. Upon removal from the press, it is found that papers could not be separated from the laminate surfaces. That is, they both had an"infinite"cling strength.

EXAMPLE 2.

Release sheets are prepared as in Example 1 sufficiently large to cover 4'X10' press plates. The release sheets are inserted between the polished press plates and the surfacing prepregs of a low pressure panel (particleboard substrate) with the coated face of the release sheet adjacent to the prepreg. Release sheets are used on the top and bottom plates.

When the press is opened and the board is ejected hot after lamination, the release sheet remains with the board and is cleanly released from the polished plates.

While still hot, the release sheet is removed from the decorative board with a cling strength of about 20 gms/5 in. The surface of the board is found to have a roughness (AA) of about 100 microinches and a 60 gloss of 6.

EXAMPLES M-0 (COMPARATIVE) The alkyl vinyl ether/maleic anhydride copolymer of Example 1, is reduced to a solution containing 20% solids in toluene and the alkyd resin component is omitted.

This solution is applied to (Example M) a commercially available greaseproof paper by gravure coating in the amount of 3.5 Ibs./ream dry. In a similar manner (Example No. N) a 35 Ib./ream glassine paper and (Example No. O) a 55 Ib./ream clay coated publication paper have 3.5 Ib./ream dry coats of the copolymer applied. Each of these sheets is then used for release purposes, as in Example A.

In the case of the coated greaseproof paper, the release occurred at a cling strength of about 25 gms. The gloss of the laminate was only 1 unit at 60 . This indicates that the copolymer is too soft to be used as the sole release coating per se. It is typical that materials which soften and flow readily under the laminating conditions will produce low gloss surfaces. A well-known example is polypropylene film.

In the case of the glassine paper and the publication paper, it was found that picking of paper fibers and/or clay coating occurred. Cling strengths were 100-250 gms./5 in. It is apparent that the copolymer is not a substance which when used alone will release from all types of surfaces.

EXAMPLE 3.

Example 1 is repeated in every detail except that the alkyl vinyl ether/maleic anhydride copolymer is replaced by an equimolar copolymer of maleic anhydride and octadecene-1, i. e. in Formula I, above, the two R groups form an oxa group and in Formula II, above, R2 is hydrogen, X is CH2, and R3 is a Cl, alkyl group. The cling strength is s16 grams/5 in.

EXAMPLE 4.

100 parts of the maleic anhydride/alkyl vinyl ether copolymer of Example 1 are refluxed with 50 parts of IN sulfuric acid at 110 C for 7 hours to hydrolyze the anhydride to the acid, i. e. RI in Formula I, above, is hydrogen. A white, soft, waxy solid separates from the media, is recovered by decantation, washed in cold water until free of sulfuric acid and dissolved in a 50: 50 mixture of isopropanol and toluene to form a solution containing 40% solids. This solution is used in the same manner as the maleic anhydride copolymer of Example 1. The cling strength of the resultant texture release sheet is 57 grams/5 in. A portion of the hydrolyzed copolymer solution is analyzed by infra-red spectroscopy and found to be 90-100% in the form of the acid.

EXAMPLES 5-7.

The alkyd resin-maleic anhydride copolymer mixture of Example 1 is applied to a series of different cellulosic sheets at 3.5 Ibs./ream add-on as described in said example. The results are set forth in Table I, below. Example 5 employs a sheet of kraft paper, Example 6, a sheet of publication stock, clay coated on one side and Example 7 a sheet of publication stock coated on both sides. Publication stock is a fine paper material usually employed in the printing of fine magazines.

TABLE I.

Example No. 5 6 7 Paper Basis Wt. (Ibs./ream) 40 46 32 Gurley Densometer (secs.) 13 1860 10,200 Apparent Density (gms./cc) 0.75 1. 22 1.02 Cling Strength (gms./5 in.) 14 21 17 Laminate gloss (60 ) 5. 0 14. 0 8. 0 AA Roughness (microinches) 100 35 85 EXAMPLES s16.

The procedure of Example 1 is again followed except that the alkyd resin used is varied as is the copolymer compounded therewith. The copolymer is set forth with reference to Formulae I and II, above. In each instance, results substantially equivalent to those shown in Example 1 are observed. The materials are shown in Table II, below.

TABLE II

Example Alkyd Rsin Copolymer R R1 R2 X R3 8 Soy fatty aicds - 40% Benzoic acid - 2% OR1 both C4 alkyl H O C10 alkyl Isophthalic acid - 38% Glycerol - 20% 9* Coconut oil - 31% Isophthalic acid - 40% OR1 both C12 alkyl H O C18 alkyl Trimethylol ethane - 29% 10 Soya fatty acids - 53% mixture of Phthalic anhydride - 27.8% OR1 hydrogen & H CH2 C15 alkyl 98% glycerine - 19.2% C12 alkyl C19 alkyl and C17 alkyl 11 Soy a oil - 45.5% hydrogen & Dehydrogenated Castor OR1 C18 - C16 H O C9 alkyl oil - 15.0% alkyl mixture Phthalic anhydride - 23.5% Pentaerythritol - 16.0% 12 Soya oil - 45.1% Isophthalic anhydride - 38.3% oxa - CH3 O C12 alkyl Pentaery thritol - 5.6% Ethylene glycol - 11.0% 13** Tall oil fatty acids - 40.4% Adipic acid - 10.5% oxa - H CH2 C1@ alkyl Trimellitic anhydride - 41.5% Propylene glycol - 38.3 % TABLE II (CONT.)

Example Alkyd Resin Copolymer R R1 R2 X R3 14 Tall oil fatty acids - 44.7% Phthalic anhydride - 32.6% oxa - H CH2 C2 alkyl Pentaery thritol - 15.9% Ethylene glycol - 6.8% 15 Soya oil - 57,0% Tung oil - 14.2% oxa - H CH2 C13 alkyl Phthalic anhydride - 19.5% glycerol - 9.3% 16 Tall oil fatty acids - 27.0% Phthalic anhydride - 38.0% oxa - H O C15 alkyl Trimethylol Propane - 35.0 % * mixed melamine - MF 5#0 Me3#7 (average methylolation and methylation) used to cross-link alkyl resin ** hexabutylated hexamethyl melamine used to cross-link alkyd resin EXAMPLES 17-21.

To 92.5 parts of an alkyd resin solution produced from 39.7 parts of soya oil, 41.3 parts of isophthalic acid and 19.0 parts of glycerol and having a solids content of about 62%, a viscosity of 23-29 secs. #2 Zohn cup. 77.0 F and a density of 8.4-8.7 lbs./gallon, in a 67/33 isopropanol/xylene solvent, and containing 50% of hexakismethoxymethyl celamine, are added 7.5 parts of a catalyst solution comprising 50% p-toluene sulfonic acid and 50% isopropanol. By means of a gravure printing cylinder having a quad cell pattern of a diagonal count of 120 per inch and a cell depth of 0.0032" uniformly knurled over its entire face, the alkyd-catalyst solution is applied to a 35 lb./3000 ft. 2 ream bleached kraft grease-proof paper at 0.1 mil thickness. The coated paper is then dried and cross-linked in a high velocity hot air oven for 30 sec. at 280 F. The coating weight, after cross-linking, is 1.8 Ibs./3000 ft 2 ream.

To the resultant coated sheet are then applied various amounts of a methyliso butylketone solution of an equimolar copolymer of maleic anhydride and octadecene-1, i. e. in Formula I, above, the two R groups form an oxa group and in Formula II, above, RI is hydrogen, X is CH, and R'is a C, l alkyl group. The second coating is applied by means of a 150 Q quad rotogravure cylinder on a Geiger laboratory printing press. The cylinder applies 0.5-0.6 parts of wet coating to the substrate. The resultant doubly coated paper is then dried at 125 C for 10 minutes to remove the ketone solvent.

The coated paper is then cut into 4'X8'sheets, placed in a press pack assembly and pressed as described in Example A except that Component B is the doubly coated paper.

It is found that the doubly coated paper releases readily from the laminate, leaving no particles of paper, resin or other debris. In order to measure the ease with which such paper is striped from the laminate, the cling Strength Test described above is performed. The results are set forth in TABLE III, below.

TABLE III

Conc. of Copolymer Cling Strength Example in Ketone Solvent Gms/5 In.

17 2 0c7C 23 18 1. 0, 7c 36 19 0. 5q 34 20 0. 2xc 37 Zt 0. 1^ 40 EXAMPLE 22.

Following the procedure of Example 17 except that the second coating is applied as a 40 /. toluene solution of an equimolar alkyl vinyl ether/maleic anhydride copolymer in which the alkyl vinyl ether is a mixture of 96% Cl, alkyl, 2% Clfi alkyl and ? % Cl,-C"alkyl vinyl ethers. The Cling Strength value is similar to that of Example 17.

EXAMPLE 23.

Release sheets are prepared as in Example 17 sufficiently large to cover 4'yin' press plates. The release sheets are inserted between the polished press plates and the surfacing prepregs of a low pressure panel (particleboard substrate with the coated face of the release sheet adjacent to the prepreg. Release sheets are used on the top and bottom plates.

When the press is opened and the board is ejected hot after lamination, the release sheet remains with the board and is cleanly released from the polished plates.

While still hot, the release sheet is easily removed from the decorative board. An excellent decorative board is recovered EXAMPLE 24.

100 parts of the maleic anhydride/alkyl vinyl ether copolymer of Example 23 are renuxed with 50 parts of 1. ON sulfuric acid at 110 C for 7 hours to hydrolyze the anhydride to the acid, i. e. Rl in Formula I, above, is hydrogen. A white, soft, waxy solid separates from the media, is recovered by decantation, washed in cold water until free of sulfuric acid and dissolved in a 50 : 50 mixture of isopropanol and toluene to form a solution containing 40% solids. This solution is used in the same manner as the maleic anhydride copolymer of Example 17. The resultant texture release sheet is easily removed from the laminate. The hydrolyzed copolymer solution is found by infra-red spectroscopy to be 90-100% in the form of the acid.

EXAMPLES 25-27.

The coatings of Example 17 are applied to a series of different cellulosic sheets as described in said example. In each instance, the results are comparable to those of Example 17. Example 25 employs a sheet of kraft paper; Example 26, a sheet of publication stock, clay coated on one side and Example 27, a sheet of publication stock coated on both sides.

EXAMPLES 28-36.

The procedure of Example 17 is again followed except that the alkyd resin used as the first coating is varied as is the copolymer used as the second coating. The alkyd resin-melamine coatings and the copolymer coatings are formed using the specific components shown in Examples 8-16. In each instance, results substantially equivalent to those shown in Example 17 are observed.

Claims (21)

WHAT WE CLAIM IS :- 1. A self-releasing coating composition comprising an organic solvent solution containing from 0.5% to 80.0%, by weight, based on the total weight of the composition, of an organic solvent soluble mixture comprising

1) from 75% to 99%, by weight, based on the total weight of (1) and (3), of an oil-modified alkyd resin, 2) from 30% to 70%, by weight, based on the total weight of (1) of a polyalkylether of a polymethylol melamine, and

3) from 1% to 23%, by weight, based on the total weight of (1) and (3), of a copolymer containing from 15 to 85 mole percent of recurring units having the formula

wherein each R is, individually, OR', R'being hydrogen orCl-C22 alkyl, or the two R groups taken together form an oxa group and the remaining units are recurring units of the formula

wherein R2 is hydrogen or methyl, R3 is a CDC30 alkyl radical and X is 0 or CH^.

2. A composition according to Claim 1, wherein said recurring units of com ponent (3) are derived from maleic anhydride and a Cl8 alkyl vinyl ether.

3. A composition according to Claim 1, wherein the two R groups are taken together and form an oxa group.

4. A composition according to Claim 1, wherein both Rl groups are hydrogen.

5. A composition according to Claims 1,3 or 4, wherein RI is hydrogen, X is CH2 and R'is a Cl5 alkyl group.

6. A composition according to any preceding Claim, wherein the polyalkylether of a polymethylol melamine is hexakismethoxymethyl melamine.

7. A composition according to any preceding Claim, wherein the alkyd resin is derived from soya oil, isophthalic acid and glycerol.

8. A composition according to Claim 7, wherein the copolymer is derived from maleic anhydride and octadecene-1.

9. A release sheet for use in the production of laminates, comprising a cellulosic paper sheet coating with a first coating (A) comprising an oil-modified alkyd resin cross-linked with from 30% to 70% by weight, based on the total weight of (A), of a polyalkylether of a polymethylol melamine, and arop said (A) a second coating (B) comprising a copolymer as defined in any one of Claims 1-5 or 8.

10. A release sheet according to Claim 9, wherein said paper sheet is grease-proof paper, glassine paper or clay-coated publication paper.

11. A release sheet according to Claim 9 or Claim 10, wherein the alkyd resin is derived from soya oil, isophthalic acid and glycerol.

12. A release sheet according to any one of Claims 9 to 11, wherein the polyalkylether of a polymethylol melamine is hexakismethoxy melamine.

13. A release sheet for use in the production of laminates comprising a cellulosic paper sheet coated with a composition comprising a mixture of: (A) from 75 to 99% by weight, based on the total weight of (A) and (B), of an oil-modified alkyd resin crosslinked with from 30% to 70% by weight, based on the total weight of (A), of a polyalkylether of a polymethylol melamine, and (B) from 1% to 25% by weight, based on the total weight of (A) and (B), of a copolymer as defined in any one of Claims 1 to 5 or 8.

14. A release sheet according to Claim 13, wherein paper sheet is grease-proof paper or glassine paper.

15. A release sheet according to Claim 13 or Claim 14, wherein the alkyd resin is derived from soya oil, isophthalic acid and glycerol.

16. A release sheet accordimg to any one of Claims 13 to 15, wherein the polyalkylether of a polymethylol melamine is hexakismethoxy melamine.

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17. A self-releasing coating composition, according to Claim 1 and substantially as described in any one of the Examples herein.

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18. A release sheet for use in the production of laminates, according to Claim 9 or Claim 13 and substantially as described in any one of the Examples herein.

19. A method of manufacturing a decorative laminate by heat and pressure consolidation of superimposed laminae between press plates, characterized in that there is positioned between each press plate and the adjacent laminae a release sheet according to any one of Claims 9 to 16 or 18.

20. A method of manufacturing a decorative laminate, according to Claim 19 and substantially as described in any one of the Examples herein.

21. A decorative laminate whenever made by a method according to Claim 19 or Claim 20.