IE39941B1 - Coating and laminating of sheets using polyurethane (urea)s - Google Patents

Abstract

1435067 Films and laminates by sintering BAYER AG 8 Oct 1974 [10 Oct 1973] 43504/74 Headings B5B and B5N [Also in Division B2] Films and laminates are formed by laying polyurethane and/or polyurethane urea on a flexible temporary support for stripping therefrom or coating a flexible permanent support by (A), applying to the support a dry polyurethane and/or polyurethane urea powder which: (a) comprises smooth, spheroidal particles; (b) has an average diameter of 5 to 200 Á; (c) has an ionic group content of 1 to 15, milliequivalents per 100 g.; (d) has an electrical resistance of 10<SP>10</SP> to 10<SP>14</SP> ohm./cm.; (e) has an intrinsic melt index (I.M.I.) curve (ASTM D1238-65T) in the shape of the ascending branch of a parabola such that the I.M.I. changes within a temperature interval of from 5 to 50‹ C. from 2 g. per 10 minutes to 50 g. per 10 minutes, and (B) sintering or fusing the powder by heat. The powder may contain Mg stearate as lubicant and C black, TiO 2 , aluminium bronze, iron pigment or cadmium pigment. Separate pigments may be used in several powders each issuing from one coating nozzle to form a multicolour film. Suitable methods of preparing the polymers are listed. The powder is preferably applied by doctor spreading and may be heated just to its melting point to produce a macroporous layer or above to produce a continuous film. In examples various two layer films are produced, one of which may be macroporous, the layers being the same or of different polyurethanes. In Examples (3) a one- or two-layer film is wet laminated to one or both sides of cotton fabric, polyester fabric or a non-woven fibre web using polyurethane solution or dispersion as adhesive, (7) a knitted cotton fabric is laminated to a two-layer film without adhesive while the film is tacky, (9) a two-layer film is laminated to a polyester/polyamide non-woven fibre web, and (10) a cotton/poplin fabric is calendered to a one-layer film. (From GB1435067 A) [FR2247328A1]

Description

39941 This invention relates to the coating and laminating of sheets using polyurethane (urea)s.

Conventional processes employed for this purpose in the textile field include e.g. knife coating, padding, spraying and calendering. In most cases, it is necessary, for technical reasons,to use coating and laminating substances which may be applied in the liquid state during the process. Exceptions to this rule include, for example, the calendering processes commonly employed in the rubber industry, flame-laminating of polyurethane foams or the application of polymer powders to sheets of all types by heat-sealing. The application of substances, such as polyethylene powders, by means of coating knives, to form backings on carpets or as floor coverings in the construction of motor vehicles is known. Apart from these exceptions, however, coating and laminating techniques depend on the use of products within a suitable range of viscosity which may be applied by technical spread-coating or spraying processes.

Thermoplastic polymers, for example, may be adjusted, to the required consistency by heating them above their melting point, e.g. when they are applied by the so-called "roller melt process". One disadvantage of this method, however, is that the polymers suffer prolonged exposure to elevated temperatures while at the same time being subjected to severe mechanical stress. Not all polymers are capablc of withstanding such severe conditions. Moreover, over a wide range of temperature 39841 the precision of the rollers, (their so-called'convex property") used Tor roller melting must be of a standard which is difficult to fulfil in practice, especially if the polymers are applied O in extremely thin layers i.e. from 20 to 40 g/m . r, A method which is widely used in practice involves dissolving the polymers in organic solvents and then applying the resulting solutions by spread-coating or spraying.

Uoth the advantages and disadvantages peculiar to these systems are well known to those skilled in the art. The In concentration of solids in the solutions for spreading or spraying is relatively low, especially in the case of high-quality products based on polyurethanes, so that considerable quantities of solvents are involved in spread-coating or laminating processes. For ecological and economic t Xrt reasons, it is necessary to recover the evaporated solvents and solvent mixtures and recycle them, preferably in a purified form, after careful refining. Furthermore, the operations required for dissolving, filtering and otherwise treating the pastes are very time-consuming and require considerable 20 commitment of apparatus.

Increasing use is being made of aqueous emulsions or dispersions of polymers for coating and laminating processes. Systems of this type are particularly interesting on account of their physiological and ecological 25 harmlessness. Their main disadvantage, however, is that very few emulsions or dispersions of synthetic polymers arc stable when frozen. In contrast to frozen solutions, e.g. of polyurothanes in organic solvents, frozen aqueous emulsions or dispersions are, in most cases, no longer usable when "50 they are thawed.

Aqueous suspensions of polymer particles, on the other hand, are stable in the frozen state. Physically, these - 3 - 39941 suspensions are unstable dispersions. The polymer particles may l>«: recovered Trum the suspension in a solid form hy decanting followed liy careful drying. These solid sulistances may l»c reconverted into aqueous suspensions or pastes whenever 5 required hy redispcrsing them in water, optionally with the addition ol' additives, e.g. thickeners, fillers or inorganic pigments.

One disadvantage of the use of aqueous pastes, however, is that a considerable amount of energy, even greater than that 10 used when applying organic solutions, is required for evaporating the water.

The coating industry is therefore very interested in obtaining systems which may be worked-up by dry processes, i.e. without any solvent or dispersing agent. 15 As mentioned above, dry powder may be applied in exceptional cases, for example for backing carpets or heat-sealing textiles.

Belgian Patent No. 77<>,'i20 describes the application of polyurethane powders by a modified electrostatic powder spray process 20 (EPS process). Apart from the fact that this requires very special and complicated mechanical techniques, it may only be used for applying powders which have very special electric properties, including an electrical resistance of not less than 10*** Ohm/cm. 25 A knife coating process is discussed, in general terms, in Belgian Patent No. 0t>*»,lt»8. The powders according to Belgian Patent No. bb'i,U>8, however, are obtained in such a form that, when applied with coating knives they may only form heaVy coats and are therefore not universally applicable. 30 There is therefore a gap in the technical knowledge relating to coating and laminating sheets, whence the demand arises for developing coating processes which do not. have the disadvantages - 4 - 3 0 0 11 descri l»c*d above.

IL has now been round that t;«rl.nin dry polyurctlmnc powders may lie applied Ity conventional, spread-coating and screening prat-esses in conventional coating plants. In contrast to what has been described in Belgian I'atcnt No. 77<>,'<20, the KI'S technique may be employed for the application oi' these powders, hut this is not essential. The present Invention differs from Belgian I'atcnt No. in that it stul.es precisely according to which particular criteria the powders must he selcctcd, for example in order to obtain either homogeneous or non-homogeneous, uniform or irregular coats having weights . 2 per unit area varying from 1<> g/m up to almost any desired thickness.

It is found that the solid particles must meet stringent requirements, especially as regards the nature of their surface and their melting characteristics.

The diameter of the particles should be from 1 to 2<>0 ji, preferably from H to 1*>0 u. The particles should have a smooth, spheroidal surface in order to ensure from the start that they will be easily spreadable and pourable.

The melting characteristics of the polymers are particularly important. It is found that the best method ol' characterising the products used in the process according to the present invention is to draw up an intrinsic melt index (1MI) curve.

To determine the intrinsic melt index, which is independen1 of time, the synthetic resin melt heated to a given temperature is forced at a given pressure through a channel (nozzle) which has a given ratio of diameter to length, and the extruded quantity, which is taken as a measure of the melt index by analogy with ASTM D 123H-(>'j T, is determined by weighing. - 5 - 309 41 If the mult index is determined in this way for varyinu preheating times, the intrinsic melt index is obtained by extrapolating to t : 0, (it is always assumed that the relationship between time and the melt index is linear). 5 This intrinsic melt index is a constant for a given material whi<-li is independent of the preheating time. This melt index is independent of time and therefore indicates what quantity of material would be extruded under given test conditions nf'er a preheating time of O minutes, if it were possible to 10 heat the material to the testing temperature in 0 minutes.

The test apparatus used in this application was onHKV l!000Bviscosim«*tnr (manufactured by fiflttl'ert of lluchcii/Odcnwald (UHD)). The nozzle in this apparatus had a length of l|5 nun, a diameter of 1.05 mm and a conical inlet with an angle ol' aper-1") ture of <>0°. The pressure exerted on the melt was 177.0 kp/c^~.

If the measurement of the tine-independent melt index is carried out at various temperatures, under otherwise identical conditions, and the values obtained are plotted as a graph, the graphs obtained are either straight lines with a characteristic 20 slope or curves.

It was found that for coating and laminating it was particularly suitable to use polyurethane powders which had melting points or melting ranges of from 110 to 250°C, preferably from 110 to 190°C. Furthermore, the IMI curves should 25 be in the form of the ascending branch of a parabola such that within a temperature interval of from 5 to 50°C, preferably from 10 to 40°C, the IMI value changes from 2 g per 10 minutes to 50 g per 10 minutes, as shown in the accompanying dlagram.Curves 2 and 5 were obtained by testing polyurethane powders which may be "50 used in the process according to the present invention, (products corresponding to Examples 1 and 3), while a powder which has the melting characteristics represented by curve 1 - 6 - 399 41 could not be used in the present process.

Polyurethane or polyurethane ureas suitable for use according to the present process must, in addition, have an ionic group content of from I to 15 milliequivalents per 5 100 g and an electrical resistance of from 10*^ to 10*^ Ohm/cra.

The present invention provides a process for forming a film or layer of at least one polyurethane and/or poly— urethane urea comprising applying the said polyurethane and/or polyurethane urea In a dry form to a flexible support or 10 substrate in the form of a pulverulent polyurethane and/or polyurethane urea which; -comprises particles having a smooth, spheroidal surface, —comprises particles having an average diameter of 15 from 5 to 200M , —has an ionic group content of from t to 1 5 mil I ie«ju i.v.il — cnUpcr 100 g, - -has an electrical resistance of from l010 to lO1^ Ohm/cm, 20 -has an IMI curve, as herein before defined, the shape of which at temperatures of from 110 to 250°C is in the form of the ascending branch of a parabola such that the IMI value, as herein before defined, changes within a temperature interval of from 5 to 50°C 25 from 2 g per 10 minutes to 50 g per 10 minutes, and then sintering or fusing the said polyurethane and/or polyurethane urea by the action of heat.

Hie polyurethane and polyurethane urea powders used according to the present process may be prepared by reacting 30 NC0- pif;polymers (containing ionic groups) with primary and/or .secondary diamines (containing aliphatically-bouml amino groups) and/or dicarboxylic acid dihydrazides in the presence oi water. The NIl/NCO molar ratio in the chain-lengthening reaction is preferably from 0.1 to 0.95, in particular from 0.25 to O.85. The ionic group content in the NC0-prepolymers is calculated so that the products of the process will have the desired ionic - 7 - 39941 group content of from 1 to 15 milliequivalents, preferably from 2 lo 10 milliequivalents per 100 g.

The powders are preferably obtained by first preparing a solution in organic solvents, of the prepolymer which contains 5 both isocyunutc groups and ionic groups, combining this solution with un aqueous solution of a chain-lengthening agent and finally removing the organic solvent, preferably by distillaLion. By employing this method, the powders used ia ^he process according to the present invention may be obtained lO in the form-of a sedimenting aqueous dispersion. i A particular advantage of this embodiment of the process is that it requires no high-speed stirrer, the NCO prepolymer may be mixed with the chain-lengthening agent simply by low-speed Stirling. 15 The above-mentioned pi'epolymcr.s which contain both free isocyanate groups and ionic groups are Known compounds lor the preparation of emulsi l'ier-free polyurethane dispersions. It is preferred to use NCO prepolymers of the type which have an average molecular weight of from 300 to 25,000, preferably from 20 soo to 15,000 and in particular from 2000 to 7000.

The properties of the resulting polyurethane urea powders may be varied as desired within wide limits by suitable measures. This applies especially to the hardness and size of the particles.

The first way of influencing the properties of the 25 powders lies in controlling the structure of the ionic prepolymer which contains isocyanate groups. This may lie achieved by known methods, (see llclgian Patent Specification Nos. 653,223 ami 730,5'o), using the stin ting materials mentioned in the said Patent Specifications. In addition to those compounds, however, 30 compounds which contain amino groups, e.g. those described in French Patent Specification Nos. l,3bl,*10 and 1,300,9*1, in German husI cgeschri 1' t No. 1,122,2V and in l!S Pati-nt Spcc i f i cu t i on - 8 - 39941 No. 2,hnk,'i>«), may also he used as higher molecular weight substances wlii«h iron La in reactive hydrogen altims.

The size ill' the parlieles is primarily determined l»y Mi»* ionle group content of Mic prepolymer. Thr hardness ol' r> the particles is primarily determined hy the chemical nature oT the palyisocyanutes or compounds containing reactive hydrogen atoms which are used for preparing the NCO prepolymers.

Harder polyurethunes may lie obtained liy restricting the? choice ol' Ihcse polyisocyanates or compounds containing reactive hydrogen II) uLoms lo those which have low molecular weighls ol up to 500, whereas softer products may be obtained by using exclusively higher molecular weight compounds having molecular wcighLs or lip lo 10,000. Mixtures, in any proportions, may lie used between these two cxLrentes. 11 Since the molecular weights of the prepolymers will not be very high because prepolymer formation is carried out using relatively large isocyanate excesses, employing a molar rutio ol' NCO groups to reactive hydrogen atoms ol" from 'i to 1.1, prcl'cruhly from 2 to l.'i, it is not necessary to have u strictly 20 linear chain structure although the NCO prepolymers used for preparing the powders are preferably linear having two aliphatically bound isocyanate end groups. i These powders are preferably prepared by reacting a solution ol' the prepolymer with an aqueous solution or 25 dispersion ol' the chain-lengthening agent. In some cuscs, however, the chain-lengthening agent, dissolved in nnorjinnic solvent, may be added while the dispersion is being formed.

The polyurethane powders to be used according to the present process may, in principle, be prepared by the conventional 30 processes described in Belgian Patent Specification Nos. 653,223 and 730,5^3 for obtaining emulsifier-free polyurethane dispersions.

Suitable chain-lengthening agents are, in particular, - 9 - 399 41 primury and/or seeondury diamines which contuin ul iphutically hound amino croups and dicarboxylic acid his-hydra/idcs (in the cast! of the lust mentioned chain-lengthening agents, it may l>o assumed thut it is primarily the amino groups in the 5 (3-position to the carbonyl groups which rcaot with the NCO prepolymers so that the dicarboxylic acid his-hydrazides may be regarded, at u first approximation, as difunctional chain-lengthening agents). Suitable diamines are in particular those ha.'ing a molecular weight below 250, e.g. ethylene diamine, 10 propylene—1,2-diamine, N—methyl-propylene diamine, hutylenc diamine, hexamethylene diamine, piperazine, 2-methyl pipera/ine, dimethyl piperazines, N,N'-dimcthyl-cthylene diamine, N,N* — diethy1—diethylone diamine, N,N'-diisopropyl—ethylene diamine, N,N'-d ime thy1-propylene-1, 2-d iamino, N,N'-d ii sopropy1-propylene-15 I,2-diamine, N.N'-bis-hydroxyethyl-ethylene diamine, N-hydroxy elhy1-othylene diamine, N-hydroxyj: ropy 1-e tliy lone diamine, N,N'-bi s-(hydroxypropy1)-e thy1ene diamine, N,N'-d i m e thy1-hexamethylene diamine, propylene-1,3-diamine, y,y'-bis-amino propyl sulphide, y,y'-bis-aminopropyl-mothylamine, N,N-bis-("y-20 aminopropyl)-aniline and N,N-bis-(y-aminopropyl)-m-toluidine. Kther diaminos, ester diamines and diamines whicb are formed hy the hydros-nation of cyunoethy luted diols or li i lime t i una 1 dihydroxy-polyes tors or dihydroxy-polyethers are also suituble chain-lengthening agents. 25 '"he diamines are used in the form of their salts, for example carbonates or ucetutcs. The salt formation may be carried out only partially, e.g. in order to improve the solubility. Salt formation on the primary amino groups results in a reduction in reactivity. 30 ihe dicarlioxvlic acid his-hydrazides used may he, for example, his-hydr&zidcs of dicarboxylic acids. the said acids having a molecular weight below 250, e.g. - to - 39941 oxidic acid, succinic acid, adipic acid, phthalic acid, litrnphlliulic acid, und tctrohydrophlhalic acid. Bis-hydrazidea of carbonic acid may also be used. Difunctional polyesters having car boxylic acid-hydrazide end groups may also be used.

Suituble solvents for preparing the products used in the present process arc, "in particular, compounds which aro miscible with water and have ' boiling point below 100°C, e.g. acetone, methyl ethyl ketone, tetrahydrofuran and ethyl acetate. Solvents which are immiscible with water may also be used, provided the reactants are sufficiently stirred to ensure vigorous mixing. Benzene and toluene are examples oi' such solvents. Solvents which have boiling points above 100°C, e.g. toluene, chlorobenzene, dimethyl l'ormamide or dimethyl sulphoxide, may also be added,but the removal of these solvents l'rom the products of the process generally requires considerable effort.

The polyurethane powders used according to the present process are preferably prepared as follows: The ionic NCO prepolymers are synthesised in a conventional manner from dihydroxyl compounds (having a molecular weight of from 500 to 5,000), diisocyanates and, optionally, chain-lengthening agents, using an excess of diisocyanate such that the adduet contains from 1 to h %, by weight, of NCO groups. In addition, the NCO prepolymer contains from 1 to 15 milliequivalents of quaternary nitrogen, carboxylate or sulphonate groups per 100 g.

Prom 30 to 90 }6, by weight, solutions of prepolymer, in acetone, (viscosity at 50°C: l'rom 30 to M000 rP), ure mixed with aqueous solutions of aliphatic diamines which contain primary and/or secondary amino groups. The acetone is then distilled oil' and the polyurethane urea powder is ol> tn i 11.-d in the form af an aqueous sedimenting dispersion. The produel of the process may be ohtuincd in the pure l'orm simply by I'il t rat ion 39841 The dry powder may be applied by the dry knife coating or screening process.

For the ch«in-lengthening reaction, one may either add, with stirring, the aqueous solution to the acetonic solution or 5 vice versa. This mixing process is preferably carried out in u continuously operating apparatus hy feeding the two solutions into a mixing vessel, for exumplc from pumps. The mixing vessel is, in the simplest ease, equipped with a stirrer and an overflow from wliieh the aqueous acetouic dispersion I'lows IO into a distillation apparatus. The dispersing temperature is from 20 to preferably from 35 to 55°C. The quantity ol' water which is required for dispersion and in which the diamine is dissolved is from O.H to 3 times, preferably from 1 to 2 times, by weight, that of the ionic NCO prepolymer. 15 For continuous mixing at a high rate of throughput, it is preferred to use high-speed stirrer apparatus or mixers which are capahlc of producing high shearing forces. Suitable apparatus for this purpose include , e.g. mixing screws mid, particularly, multi-shaft screws, internal mixers, high-20 pressure or low-pressure mixing chambers with counterflow mixing or ultrasonic dispersers, all of which are well known to those skilled in the art. When using such apparatus, it is preferable to work with from 70 to yo % solutions, or even completely without solvents if the prepolymers are 25 sufficiently fluent.

The properties of the polyurethane powders which are first obtained as suspensions may be influenced as desired, not only by the chemical composition of the polyisocyanate pre- Dolymcr. but also l»y the conditions under which dispersion 30 is carried oub. The most important factors are the nature and quantity of the chain-lengthening agent, the quantity of water, the nature and quantity of organic solvent, the pll and Die 399 4 1 reaction temperatures which may ho varied from ()°C to the boiling point of Ihe organic solvent, and, it' desired, an elevated pressure aay also he employed.

Another important 1'actor is the method employed for 5 mixing the aqueous and organic phase, i.e. whether these two phases are introduced practically simulLaneousiy, e.g. in a continuously operating mixing apparatus, or whether the organic phase is added lo the aqueous phase or vice versa. It must he repealed, however, that suitable products may also he 10 obtained, for example, by running the aqueous phase into the organic phase while stirring with an ordinary stirrer. During or after the mixing of the two phases, the organic solvent is removed by distillation. The finished powder is obtained from the resulting aqueous polyurethane 15 dispersion by filtration.

The polyurethane powders may be applied by the conventional doctor coating processes, i.e. using fixed doctor coating systems, e.g. floating knife coating systems, rubber blanket couting systems and, especially, doctor roll coating,as well as roll 20 coalers or reverse roll coalers.

It is surprisingly found that polyurethane powders which have the required properties for use in the present process may even be doctor coated in the dry state hy methods which industrially may otherwise only be employed for pasty mixtures 25 which may he spread-coated.

The powders are so line and readily pourahle that, without any further additives or additional grinding, they are able to pass through the finest no/./.] c of the glass nozzle series lor determining the pourability according to the "l)E(IIJSSA 30 system" ("Degussa" is a ' Trade Mark).

If desirtfd, a further improvement may he ohtuincd hy adding small quantities of magnesium stcarat.c and other conventional - 13 - 39941 lubricants. Tho quantities added may be from 0.1 to r>%, based on tho total solids content.

Tho ease with which these powders may be poured is surprisingly high oven whon they havo a residuul moisture 5 run tonLt hound by adsorption, of from 0.5 to 5.0jt by weight. This residual moisture content may even l>o desirable hncaiisc those small quantities of water have the ei'l'oet ol plasticising the synthetie resin and slightly reducing the melting point ol' the products. 10 Both direct coatings and, preferably, reverse coatings may be obtained according to the present process. Reverse coating is preferably carried out ut-«iig a separating support of silieone-Lreated rubber or, more preferably, a steel he] I. although conventional separating papers may, ol° course, also be employed. 15 The thickness of the coatings obtained is generally from 10 to 100 g/m , although the coatings may be thicker. 11' the powders applied by coating or screening are immediately exposed to heat, e.g. in an IU field, and suddenly heated to temperatures above their melting point., 20 they fuse to form homogeneous foils. 11", on the other hund, the dry powders applied to their supports are heated slowly and only up to the melting point, the resulting layer which will hereinafter be referred to as frit has a macroporous structure. 25 The coating may be coloured or pigmented by various methods, preferably by mixing the polyurethane powders with pulverulent pigments or fillers, e.g. carbon black, titanium dioxide, aluminium bronze, (a pigment of pure aluminium which has the aspect of bronze), iron pigments or cadmium pigments, before they are applied. - 14 - 39941 The following Examples illustrate the invention.

Example 1 A polyurethane powder In prepared uccording to Example 7 oT Itolglun Patent Sped fication No. H00,1H5, (spherical 5 particle.s having an average diameter of '>3 yi melting point 145°C; electrical resistance 5 * 1011 Ohm/cm; IMI values) curve 2 in accompanying drawing.

The polyurethane powder is applied at a thickness ol* 100 g/m*" to u separating paper by knife coating and then exposed 10 to a temperature oJ* l'i()°C in a nozzle duct 12 m in length through whieh it is passed at the rute of 1.5 m. A tough elastic frit is formed which may easily be separated from its support and handled without any other support.

Example 2 15 The frit prepared according to Example 1 is coated with a second coat of the same powder, (thickness 60 g/m2), and then passed through a duct at 170°C as described in Example 1, A homogeneous transparent film is obtained which has a total l) thickness of 160 g/m*", high tensile strength and good elastic 20 properties.

Example 3 A powder according to Example 11 ol' Belgian Patent Specification No. «00,1«5, (melting point: 165°C, average diameter or spherical particles 61 ji, electrical resistance: 25 1011 Ohm/cm, IMI values: curve 3 in accompanying drawings,is applied to a steel belt by knife coating to form a layer 0.3 mm thick which is then fused in a nozzle duct at a temperature of 175°C to form a film:- In a second coating operation, the powder described in-^Exapple 1 is applied at a thickness of 0.3 mm 30 and then sintered by exposure to a temperature of lfi5°C to form a. frit which adheres firmly to t.he previously formed film. - 15 - 39941 The two layers may no longer be separated by mechanical methods without destroying them.

The films formed according to Examples 1 to 3 may be bonded by conventional methods of wet laminating to one or 5 more sides of any suitable support materials, e.g. cotton fabrics, polyester fabrics and non-woven fibre webs.

Polyurethane solutions or dispersions, for example, or other adhesives muy be used for wet laminating. Alternatively, laminating may also be carried out by the method of heat-i() sealing using thermoplastic resin, powders.

Example ;i A porous film, prepared according t.o Example 1, is covered with a layer of polyurethane powder from Example 1 (applied O 1*5 In a Lhickiirss of HO g/m~) by doctor coating ami exposed l.o a temperature of l'i5°C. While still in a plastic stale, the powder is laminated to a cotton-nettle fabric (80 g/m") under pressure. When cool, the laminate is firmly bonded and capable of withstanding more than 1,000,000 bends in the Dally 20 i'lcxomcter.

Example 5 100 g of the polyurethane powder according to Example 1 and 10 g of titanium dioxide are mixed mechanically and 25 applied to a silicone-treated separating runner by means of a roller coater. The layer is exposed to a temperature of lb0°C in the duct described in Example 1. A white, coherent film is obtained which is mechanically stable after cooling. 30 Example 6 a) 100 g of Ur6 polyurethane powder accordinu l.o Example I and 5 g of carbon black - 16 - 39941 arc mixed; h) 100 k oT polyurothanc powder according to Example 1 and 2 x ot aluminium bronze are mixed; 5 c) 100 g of polyurethane powder according to Example 1 and 5 g of cadmium red pigment are mixed.

Mixtures « and fc) are simultaneously applied to a steel ithree different. bolt fromVnozzies which are adapted to dispense solids and 10 which traverse the whole width of the support. The layer of mixtures applied is subsequently calibrated when the belt passes through the gap of a knife coater, und the mixtures are irregulurly mixed at the boundary zones.

After cooling and separation from the steel hell., u 15 continuous, mechanically stable film is obtained with colour effects in the form of obliquely running stripes fading out at the boundaries. Although the thickncss of the film is rendered uniform by its pussage through the gap of the uoatcr, components fe), 0^ and fc) become intermingled at the boundaries 20 of their respective zones so that a localised individual pattern is formed there within a uniform overall appearance.

Example 7 The mixtures of powders prepared according to Example 6 25 are applied as described in Example 6 except that the powder applied is not spread out completely flat. The film obtained not only has the colour effect of the products described in Example 6,but also irregularities on the surface which resemble an irregular flat embossed pattern. 30 Example 8 Preparation of the polyurethane powder: - 17 - 39941 A prepolymer is prepared by reacting 950 g dehydrated polyester of butanediol/adipic acid, which has an average molecular weight of 2190, 166 g hexane-1,6-diisocyanate and H.H g N-taelhyl-dic thanolamine for 1 hour at 100°C. 5 (>.h cc dimethyl sulphate and u total of 12H0 g acetone arc added to tho prepolymer. A 50 $ acutonic prepolymer solution which has an NCO-content of 1.23 1> is obtained.

A polyurethane urea suspension is obtained by mixing 757 parts of this prepolymer with 189 parts of a normal aqueous 10 propylene-1,2-diamine solution and 56b g water. After removal of the acetone by distillation, filtering, washing and then drying, a polyurethane urea powder which has a melting point of from 168 to 17^°C is obtained.

The powder consists of spherical particles having an 15 average diameter of 60 y and an electrical resistance of I0ia Ohm/cm. p The powder is applied to a thickness of 100 g/m to u steel belt and sintered to form a film hy heating it to 200°C. i) 20 A second coat (60 g/m") of the polyurethane powder described in Example 3 is applied to this film. The holt. with the material on it is passed through an IR field, 1.5 m in length, at the rate of 1.5 m per min.

The IB field has a total output of 2k kW over its length 25 and is so formed that the surface temperature measured on the separating support is 200°C.

After its passage through the IR field, the film is immediately laminated to a knitted cotton fabric. The application of the film is controlled by the gap so that 30 width of gap i thickness of textile + thickness of layer - 0.1 mm. The reverse .costing stripped from the steel belt has excellent' properties. - 18 - 39941 Example 9: A polyurethane powder which is a different sieving fraction of that used according to Example 3> consisting of spherical particles a diameter of 25v and having a 5 melting point of 165°C and having an electrical resistance of 10** Ohm/cm, is applied by a screen to a steel belt (thickness of application 80 g/m ) and then passed through an IK field as O In Example 8. In a second operation, a thin layer (40 g/m ) of the polyurethane powder from Example 1 is applied to the 10 resulting homogeneous film. The coating is sintered to form u frit and while still plastic it is laminated to a non-woven web of polyester/polyamide fibres. An excellent bonded material is obtained in this way.

Example 10 15 The polyurethane powder described in Example 1 is applied 2 to a thickness of approximately 100 g/m to a cotton poplin material, suddenly heated to from 180 to 200°C in an lit field (see Example 8) and then immediately cooled. It is then calendered under a pressure of 7 tons at 110°C. A direct 20 coated textile with a smooth surface is obtained.

Example 11 The polyurethane powder described in Example 3 is applied o by knife coating to a thickness of approximately 160 g/m to a steel belt and sintered in the conventional manner. While 25 the material is cooling, but still plastic, a cotton net fabric is placed on it. A second coating, this time consisting of the polyurethane powder described in Example 1, is then applied by knife coating to a thickness of approximately 150 g/m2.

This coating is also sintered in an IR field, cooled and 30 calendered. A self-supporting, stable material is obtained which may be used, for example, as a conveyor belt. - 19 - 39841 Example 12: The polyurethane powder described in Example 3 is applied.to a steel belt and sintered in the conventional manner. While still plastic it is passed under a V v 5 calibrating device consisting of a doctor knife or doctor knife or doctor roller with displaceable surfaces. The calibrating device is adjusted to be from O.Ol to 0.05 mm lower than the total thickness of the layers of ateel belt plus sintered powder. The melt is in this way 10 spread out homogeneously and calibrated.

Example 13: The polyurethane powder described in Example 3 is applied by knife coating to a steel belt at room temperature. Sintering and melting of the powder are carried out not 15 by direct heat transfer as in Example l, (nozzle duct), or as in Example 8» (IR field), but by a method of indirect heating which consists of first heating the steel belt with hot air and then heating the powder to the point of sintering and melting by heat transfer from the steel 20 belt. - 20 - 399 4 1

Claims (9)

1. CLAIMS 1. A process for forming a film or layer of at least one polyurethane and/or polyurethane urea comprising applying the said polyurethane and/or polyurethane urea in a dry form to a flexible support or substrate in the form of a pulverulent polyurethane and/or polyurethane urea which: •comprises particles having a smooth, spheroidal surface, -comprises particles having an average diameter of from 5 to 200 V. -has an ionic group content of from l to 15 milliequival ents per 100 g. -has an electrical resistance of from l0*° to lO1^ Ohm/cm,;-has an IMI curve, as hereinbefore defined, the shape of which at temperatures of from li0 to 250°C is in the form of the ascending branch of a parabola such that the IMI valitc, as hereinbefore defined, changes within a temperature interval of from 5 to 50°C from 2 R per 10 minutes to 50 g per lO minutes, and then sintering or fusing the said polyurethane and/or polyurethane urea by the action of heat. 2- A process as claimed in claim l in which the average diameter of the said particles is from 8 to l50p.;3. A process as claimed in claim l or claim 2 in which the said IMI curve is determined at temperatures of from 110 to 190°C.;4. A process as claimed in any of claims I to 3 in which the said IMI value changes from 2 g per ]0 minutes to 50 g per minutes over a temperature range of from 10 to 40°C.;39941;10;15;20;25;30;5. A process as claimed in any of claims 1 to 4 in which the said polyurethane and/or polyurethane urea film or layer is calendered after it has been sintered or fused;6. A process as claimed in any of claims 1 to 5 in which the said polyurethane and/or polyurethane urea has an ionic group content of from 2 to 10 milliequivalents per 100 g.;7. A process as claimed in any of claims 1 to 6 in which the said polyurethane and/or polyurethane urea also comprises at least one lubricant.;8. A process as claimed in claim ^ in which the said lubricaitt(s) is (arc) present in quantities of from u.l to 5%i based on the total solids content.;9* A process as claimed in claim 7 or claim 8 in which the said lubricant comprises magnesium stearate. 10. A process as claimed in any of claims 1 to 9 in which the polyurethane and/or polyurethane urea also comprises pulverulent pigments or fillers. 11. A process as claimed in claim 10 in which the said pigments and fillers are selected from carbon black, titanium dioxide, aluminium bronze, iron pigments or cadmium pigments. 1

2. A process as claimed in any of claims 1 to 11 in which the said polyurethane and/or polyurethane urea has a residual moisture content, bound by adsorption, of from 0.5 to 5-0/6, by weight. 1

3. A process as claimed in any of claims 1 to 12 in which the said flexible support or substrate is a textile, a silicone-treated rubber, a steel belt and a conventional separating paper. - 22 - 30941 1

4. A process as claimed in any of claims l to 13 in which a direct or a reverse coating is formed. 1

5. A process as claimed in any of claims l to 14 in which the said film or layer is formed on one or t more faccs of the said support or substrate. 1

6. A process as claimed in any of claims 1 to 15 in which a laminar structure is produced. 1

7. A process as claimed in claim l substantially as herein inscribed. 1

8. A process as claimed in claim i substantially as herein described with reference to any one of the Examples. 1

9. A polyurethane and/or polyurethane urea film or layer when produced by a process as claimed in any of claims 1 to l8. 20. A material comprising a polyurethane and/or polyurethane urea film or layer when produced by a process as claimed in any of claims 1 to l8. F. R. KELLY & CO. AGENTS FOR THE APPLICANTS. - 23 -