CA2310605A1 - Method for producing a thermoplastic coating and articles constructed therefrom - Google Patents

Abstract

This invention relates to a non-contact coating method for producing a substantially continuous coating and articles constructed therefrom. This invention further relates to a non-contact slot coating method for producing a variety of coatings and laminations. This invention particularly relates to a method of coating a non-porous substrate including film, foil and paper with a molten thermoplastic composition which reduces streaking caused by particles such as impurities, fillers and superabsorbent polymers. This invention further relates to thermoplastic compositions useful in the present noncontact coating method.

Description

WO 99118048 PCTIEP98/OI588 ..
METHOD FOR PRODUCING A THFRMOPLASTIC COATING AND ARTICLES CONSTRUCTED
THEREFROM
Field of the invention This invention relates to a non-contact coating method for producing a substantially continuous coating sad articles constructed therefrom. The invention further relates to a aoa-contact Blot coating method for producing a variety of coatings and laminations. This invention particularly relates to a method of coating a Substrate including film, foil and paper with a molten thermoplastic composition which reduces streaking caused by particles and enables film-to-film, film-to-foil and film-to-paper or board laminations with noareactive hot melt adhesives.
Background of the invention Conventional slot nozzle coating of molten thermoplastic ca~mpositions onto substrates is typically done by keeping the slot nozzle in contact with the substrate such that the nozzle lies on the substrate during the coating. It is unproblematic to coat hot melt adhesives at low coating weights provided that the coating need not be comxpletely closed, i.e. nonporous. Ia the context of this specification. acontinuous'" may be used to describe a completely closed, i.e. nonporous film or coating. If, however, a completely closed, i.e. nonporous coating is to be created, this can only be dose using customary coating methods if the coating weight of the hot melt is substantially higher.
Such high coating weights are expensive. Furthermore.
direct coating with a slot nozzle provides substantial mechanical sad thermal stresses on the coated substrates, especially since the slot nozzle is heated during coating.
Therefore, very sensitive substrates such as plastic films can not always be coated with a hot melt from a slot nozzle in a customary manner without damaging the substrate..
Further, the high coating weights of this prior art lead to increased stiffness of the coated substrate.
WO 96/25902, published Aug. 29, 1996, assigned to the H.B.
Fuller Co. is 8t. Paul, 1~T teaches a method of coating wherein certain thermoplastic compositions are thermally made flowable sad released from a coating device as a continuous coating without contact between the coating device and substrate being coated.
The present invention resides in specific adaptations to this novel coating method for use is a variety of other applications involving coatings oa nonporous materials and coatings oa porous materials. One type of such application is coatings on nonporous materials such as films.
Thermoplastic compositions often contain unmelted particles either in the form of impurities such as contaminants sad char or alternatively is the form of a particulate ingredient such as filler sad additives. Whey these particles are of appreciable size and/or the slot nozzle has a relatively small gap, the particles Lead to accumulate is the coating device interfering with the deposition of the coating. The particles block the passage of thermoplastic material causing a corresponding striation or streak to form on the substrate being coated. This problem is particularly prevalent is the formation of very thin coatings particularly when the optical quality is of importance such as for high quality graphic art applications, especially where films have to be coated. Accordingly, industry would find advantage in a coating method which rectifies these wo ~nsoas Pc~r~r9sioisss .

problems.
It is therefore an important object of this invention to provide a new coating method especially suited for coatings oa films, foils, paper and other such materials, which makes it possible to avoid streaking and striation problems, especially at very low coating weights.
It is another important object of the iveation to provide a coating method which permits laminations and coatings to be carried out ,.ialiae'" or "offliae", using thin films, metallized foils, heat-sensitive materials and other sensitive substrates at reduced risk of obtaining faulty or flawed products.
It is yet another important object of the iventioa to make film-to-film and film-to-foil laminations available which do not require the use of reactive adhesives.
Another abject of the invention is to provide improved coating methods for coating thermoplastic com~positioas, especially hot malt adhesives, onto porous substrates such as textiles.
These and other objects sad advantages of the invention will become more apparent from the follov~ring discussion.
Summary of the invention The present invention is a method of coating a substrate with a thermoplastic composition employing a non-contact coating method and articles constructed therefrom. The method produces a substantially continuous coating. The method is useful for a variety of adhesive and coating WO 99/28048 PCT/EP98/01588 -.

applications and particularly those which employ conventional slot coating techniques, heat sensitive substrates, require low coating weights, and/or employ thermoplastic compositions comprising particles.
In one aspect, the present invention is a method of coating wherein a certain thermoplastic composition such as a hot melt adhesive which has bees thermally made flowable, is released form a coating device onto a noaporous substrate as a substantially continuous coating without contact between said coating device sad said substrate, sad subsequently disposed upon the surface of the substrate.
Ia another aspect, the present invention is a method of coating wherein a certain thermoplastic composition such as a hot melt adhesive which has bees thermally made flowable, is released form a coating device onto a substrate as a substantially continuous coating without contact between said coating device and said substrate, and subsequently disposed upon the surface of the substrate, wherein the distance between the coating device and the substrate is greater than 20 mm.
In another aspect, the present invention is a method of coating wherein a certain thermoplastic composition such as a hot melt adhesive, which has been thermally made flowable is provided in the form of a substantially continuous noaporous film without contact of the film with a substrate, sad said film is then coated onto a substrate by means of either a release-coated roller in direct contact with the adhesive film, said roller nipping said adhesive and said substrate, or with a release coated second substrate being disposed upon the surface of the thermoplastic composition which is not is contact with the first substrate, or by a transfer-coating method, wherein a certain thermoplastic 5 composition such as a hot melt adhesive which has been thermally made flowable, is released from a coating device e.g. onto a release coated roller as a substantially continuous coating, i.e. a nonporous film, without contact between said coating device and said roller, and subssguantly disposed upon the surface of a substrate.
Ia another aspect. the presaat invention is a method of coating wherein a cartain thermoplastic composition such as a hot melt adhesive which has been thermally made flowable, is released from a coating device onto a first substrate as a substantially continuous coating without contact between said coating device and first said substrate, and subsequently disposed upon the surface, wherein said coating is subsequently rsheated and then contacted to a second substrate.
The invention further relates to utilizing this method for lamination, especially laminating of materials such as transparent film material, to a substrate, especially a printed paper or cardboard substrate as well as film to film and film to foil laminations, which avoids the above-mentioned disadvantages of the prior art and makes it possible to use noareactive hot melt adhesives for such film-to-film and film-to-foil laminations.
For heat sensitive substrates, the thermoplastic comnpositioa~
is preferably coated at temperatures of less than about 160°C, even more preferably less than about 125°C, and most preferably less than about 110°C to reduce the heat-induced stresses oa the substrates being coated. Alternatively, the distance between the coating device and the substrate to be coated may be increased such that the molten thenaoplastic composition has sufficiently cooled prior to contacting the heat sensitive substrate. This is particularly advantageous for coating and mutually bonding thermally sensitive substrates.
The thermoplastic composition preferably exhibits certain theological characteristics such that the c~lex viscosity at high shear rates (1,000 rad/sec) is less than about 500 poise and the complex viscosity at low shear rates (1 rad/sec) is leas than about 1,000 poise at the coating temperature. Some neat thermoplastic resins are suitable for tha method of the present invention provided the uncompouaded materials are sufficiently low enough in viscosity. However, compounded hot melt adhesives are preferred due to the ability to independently control the viscoelastic properties, open time, etc. Compounded hot melt are also advantageous to insure adequate adhesion to the carrier substrate or for delayed detackification of the coating after adherence to the substrate.
The resulting coating produced fro~aa said method is useful for a variety of applications wherein a consistent nonporous substantially continuous coating is desired. Coating weights of less thaw about 50-60 g/mz are preferred and even more preferred are coating weights of lass than about 30 g/ms of the thermoplastic composition due to reduce expenditure and improved tactile quality of coated substrates. Coating weights of less than I0g/mZ can is many cases be achieved.
The resulting coating is preferable for producing laminations to paper or cardboard, especially to printed paper. The coating method is particularly advantageous for manufacturing as it employs fewer production steps than prior art coating methods. Improving productivity as well as reducing the coating weight mass per area results in coatings and corresponding articles that are less expensive WO 99J28048 PCT/EP98/01588 .

than prior art.
The coating methods are however sot restricted to applications involving aonporous substrates. The inventive coatings can also be used on porous substrates. Herein, various aspects of the invention can be employed, including a method where the thermoplastic composition is released from a coating device with the distance between the coating device sad the substrate greater than 20 mmn, sad including the method of sipping a hot melt adhesive preformed film to a porous substrate by mesas of a release coated roller is direct contact with the adhesive film.
Articles as described herein comprise articles which have at least one first layer wherein said first layer is a aoaporous substrate and at least one second layer wherein said second layer is a coating or adhesive layer produced from the coating methods described above.
Brief description of the drawings Figs. 1-10 depict some of the preferred embodiments of the method of the present invention wherein a substantially continuous thermoplastic coating is formed and adhered to a substrate.
More specifically, Fig. lA shows the basic structure of a coating sad laminating machine useful for operating the invention;
Figs. 1B and 1C show the basic structures of similar such machines;
Figs. 2-4 illustrate inventive laminations at different positions of the coating device;
Figs. 5A Gad B illustrate a lamination Gad a trsasfer-coatiag method according to the invention;
Figs. 6-10 illustrate laminations, including adhesive reactivatioa laminations, in accordance with the invention.
Detailed description of the invention In the method of the present invention, a molten thermoplastic composition, such as a hot melt adhesive, preferably substantially air-free, is initially provided in the form of a substantially continuous, aoaporous "filmw which is only later contacted with a substrate, a transfer roller or some other kind of.support. Generally. the composition is released from a coating or release device in such a way that it exits the device as a substantially continuous film. A typical coating device is. a slot nozzle, as it has previously bees used for coating is direct contact with substrates. Thus, hot melt coating devices which are already known can be employed is accordance with the method of the present invention is that the slot nozzle is lifted off the substrate and is adjusted to have a suitable distance from the substrate.
As the flowable molten adhesive or thermoplastic composition exits the coating device, it does not contact the substrate, but rather travels for a distance as a continuous film suspended between the coating device and the substrate. The coating device may be initially contacted to the substrate in order to anchor or adhere the thermoplastic composition to the substrate provided that substrate will not be thermally or mechanically damaged by the contact with the WO 99/28048 ' PCTlEP98/01588 _ coating device. Alternatively, the thermoplastic composition exits through the nozzle as a substantially continuous film and descends until contacting the substrate.
The leading edge of the advancing substantially continuous film of thermoplastic composition adheres or anchors to the substrate upon contact with the substrate. Ia the case of heat sensitive materials, it is advantageous to advance the substrate by means of the drive rolls prior to contacting the thermoplastic composition to the substrate to avoid a build up of molten material which will melt through the substrate.
Machinery suitable for operating the inventive methods is shown schematically in Figures lA, 1B and 1C. Figures lA
and 18 show as embodiment where a thermoplastic co~mpoaition is released from a coating device (3) onto a first substrate (1), sad a second substrate (4) is then disposed upon the free surface of the coated adhesive, by a nip roll (5). It is to be understood that this arrangeDneat can be modified in other embodiments and especially that the second substrate (4) seed not be used is all cases. Then, the nip roll (5) can be employed to nip the thermoplastic composition directly to the first substrate. For such embodiments, the nip roll (5) will be release-coated, e.g. may be a steel roller with a polytetrafluorethyleae surface layer.
More specifically shown in Fig. lA and 1B, Substrate 1 (1) travels past a series of idle rollers (2) to ensure the web is in proper alignment prior to approaching the coating device (3). Substrate 2 (4) is optionally adhered to the coating surface by means of a nip roll (5). Substrate 1 is defined as the first substrate that is contacted with the substantially continuous thermoplastic film. Substrate 1 may be any substrate which is generally provided in a roll good such as nonwoven, paper including release-coated paper, wo ~nsoas Pcr~e~so~sss zo 5 sad a wide variety of films, foils and other materials. The eatbodimsat of Fig. lA. where the nip roll (5) is located fairly remote froma the contact point of adhesive film sad first substrate, is especially suited for the coating of porous substrates. The embodiment of Fig. 1B is especially 10 suitable when Substrate 1 is noaporous meaning air does not readily pass through the substrate. In the case of film lamination, Substrate 1 is typically a film. Substrate 2 may also be provided is a roll good and be the same or a different material as Substrate 1. 8owever, Substrate 2 may 15 also be a particulate substance such as superabsorbeat polymer, or a release-coated web material that can be pulled off the adhesive coating.
Fig iC shows an embodiment where the adhesive film is first 20 sipped onto the first. substrate (1) by nipp roll (5), which is part of a nipping station as later shown by rolls A and B
in Figs. 2-10.
A second substrate 4 is then disposed oa the free surface 25 not is contact with the first substrate (1), at a lamination station formed by foils C snd D.
Figs. 2-10 illustrate various preferred embodiments of the present invention wherein as extruded thermoplastic 30 composition such as a hot melt adhesive is applied to a first substrate sad then laminated to a second substrate.
In each of these illustrations, Substrate 2 is optional in that the invention in its broadest aspect is simply a single continuous nonporous film formed from a non-contact coating 35 method and coated onto a single substrate. In the absence of the second substrate, Figure 58 represents a transfer coat application since the molten composition is first applied to a release coated roller which then contacts a first substrate at the nip.

wo ~nso4s rcrn~~sroisss _ 5 In embodiments where the thermoplastic coating or hot melt adhesive is contacted to a first substrate in the absence of a second substrate, as illustrated is Figures 6 and 7, or is the case when the second substrate is porous. it is important to have a release coating such as silicon, Teflon, 10 or release paper oa the rollers? in contact with the adhesive or porous substrate to prevent adherence of the thermoplastic composition to the roller. The nip roller presses the air out from between the thermoplastic coating film sad the substrate to insure there is no air entrapment 15 between the first substrate and the thermoplastic composition. Roller A can be a steel cylinder to encourage heat transfer whereas collar H, typically the nip roller is rubber. Ia some cases it can be more preferred that roller A is rubber whereas roller H is a steel cylinder with as 20 external release-coating.
Figs. 3-10 demonstrate that the nozzle position may be varied from perpendicular positions to parallel positions with rsspect to the position of the substrate.

Figs. 8 sad 9 illustrate a second substrate being laminated to the first substrate at a position farther from the coating device. Ia this embodiment, it is preferred that roller C be heated to reactivate or extend the open time of 30 the hot melt adhesive or thermoplastic coating prior to being laminated to the second substrate. The temperature of roller C can vary between about 30-100°C for lamination between rollers C and D. Alternatively, roller C may be a chill roll to hasten the speed of set of the thermoplastic 35 coating or hot melt adhesive. This can be useful where the laminate is produced for intermediate storage. The substrate laminated in the nip of rollers can be either is web form, or in the form of sheets. As shown in Fig. 10, where roller C is a chill roll, the inventive method can be used to wo ~nsoas PcTn~~sioisss 5 produce substrates such as films coated oa one side with a thermoplastic comapositioa, which can e.g. be used for heat sealing applications. There this is desired, a further layer of a release paper can of course be added. as shoam in Fig.
9, to protect the heat-sealing material e.g. for 10 intermediate storage.
The coating device is positioned at a distance of at least 0.5 mQt, preferably at least 2 mm, from the substrate (or the release coated roller in the case of transfer coating is the 15 absence of a second substrate - Fig. 58). The maximum distance the coating device may be positioned from the substrate is only limited by practicality, particularly when the coating device is positioned substantially vertically.
Preferably, the distance is less than about 5 m. preferably 20 less than about 3 m, more preferably less than about 1 m, even more preferably less than about 500 mm, and most preferably from about 2 to 20 mm, depending on the properties of the thermoplastic composition being coating.
It is typically advantageous that the area between the 25 costing device and substrate be shielded during coating from air-borne contaminants and sir currents to prevent distortion of the coating prior to contacting the substrate.
This is particularly the case when the distance between the coating device sad substrate is greater than about 500 mm.

The distance is largely dictated by the viscosity and open time of the thermoplastic composition being coated. In the case of producing barrier films is this manner, it is surmised that the thermoplastic composition cools 35 sufficiently in its suspended state such that it has built in viscosity and cohesive strength to the extent that nay filaments or fibers present on the substrate surface cannot penetrate the coating, yet the thermoplastic composition is molten enough to adeguately adhere to the substrate. The 5 greater the distance between the coating device and the nip roller, the more the hot melt adhesive or coating will cool prior to contacting the first substrate. For some adhesive coa~cpositioas, this cooling will adversely affect the adhesion (or anchorage) to the substrate. Therefore,~the 10 substrate may be passed over a heated roller prior to being nipped, or a heated nip roller may be employed if the distance between the nip roller and the coating device causes the coating or adhesive to cool to the extent that it will no longer adequately adhere or anchor to the substrate.
The coating may contact the substrate at any angle (compare e.g. Fig. 3 and 4). However, it has been shown to be especially advantageous for some applications such as for barrier films, that the coating later contacts the substrate 20 in a substantially horizontal direction as is Fig. lA, 1B, 2, 6 and 8. To accomplish this, a roller can be provided in the path of movement of the substrate to give the substrate a substantially vertical, upward direction, as the substrate passes the coating device. Additionally, the coating 25 device. such as a slot nozzle, can be provided.substantially horizontally beside the roller so that the coating travels from the side towards the surface of the substrate.
The diameter of the coating rolls is preferably about 15 mm 30 to about 50 mm in diameter with the nozzle slightly above the center of the coating roll such that the angle at which the thermoplastic coating contacts the substrate is less than about 60° as the substrate is moving away from the nozzle. The coating head is adjusted by one of ordinary 35 skill is the art to optimize for even flow and distribution of the thermoplastic coating over the entire width of the application.
Thereafter, the sufficiently cooled coating contacts the 5 substrate surface and adheres to the surface without deeply penetrating into the substrate. If the thermoplastic coating is of such a ca~mposition that it substantially detackifies after sufficient cooling, the laminate of the coated substrate, thus formed, can be rolled up and stored.
10 Alternatively this can be achieved by placing s release coated second substrate, such as a silicone-coated paper, oa the surface of the adhesive costing. The laminate can then be used at some later time. The laminate can be bonded by any suitable bonding technique including ultrasonic bonding, 15 heat sealing, or more commonly adhesive bonding.
Preferably, the coating is done "inliae" immediately before nay further processing. An example of an in-lice process for which the invention is particularly well suited may be 20 found is D$ 195 46 272 C1 to Billhiifer Maschinenfabrik C3mbH, incorporated herein by reference. The surface of the coating layer which is pointing away from the substrate may be sufficiently tacky such that it can be used as a construction adhesive or for lamination to other substrates 25 and therefore can also serve to bond the coated substrate to another substrate layer. Other substrates that may be simultaneously bonded or laminated is this manner include absorbent. superabsorbent polymer, elastomeric strands or webs, tissue, films, foils, paper, cardboard, metal, as well 30 as various permeable coverstock materials such as noawoven or perforated films. These materials may be in the form of roll-goods, sheets, or particles.
In a preferred embodiment, the substrate to be laminated is 35 paper or cardboard, especially printed paper, processed photographic paper or printed cardboard, as used in the production of e.g. book covers, picture postcards, calendars, posters, high quality packaging materials, gift-wraps and so forth. The laminating material can be 5 synthetic film material, paper, textile material or any other flexible laminating material suitable for lamination.
Preferably. the laminating material is, however, s synthetic film material, especially a clear and transparent film material as is customarily used for such laminations.
Typically such film materials comprise plane or embossed films. which are at least substantially made from oriented polypropylene. polyethylene, polyesters such as MylarC~, polyacetate, nylon, celluloseacetate, and so forth having a 15 thickness of about 5 microns to about 50 microns. These films are commonly laminated or sealed to printed paper or boardstock. Composite materials are commonly produced including film to film sad film to foil and metallized substrates are comomoaly used for laminates. These types of 20 laminates are commonly found is such industries as graphic arts and packaging. Using the method of the invention, such laminates can be produced using nonreactive hot melt adhesives instead of the commonly used reactive adhesives.
25 Generally, the exit temperature of the thermoplastic composition will be lass thaw about 240°C, and thus much lower than typical polymer extrusion temperatures, which are of the order of 300°C. Although the temperature of the thermoplastic composition as it exits the coating device may 30 range from about 80°C and about 180°C or more. the noa-contact coating system of the present invention allows coating to be accomplished at extremely low temperatures.
For this embodiment it is preferred that the thermoplastic composition be coated at a temperature less than 160°C, more 35 preferably less than about 140°C, even more preferable less than about 120°C and even more preferable less than about 110°C. As mentioned previously. heat sensitive materials can also be coated is this manner by employing higher coating temperatures in combination with increasing the 5 distance between the coating device and the substrate to be coated to allow for sufficient cooling. Materials which are normally too sensitive mechanically and/or thermally (e. g.
very low gauge films) for customary coating methods can therefore be coated using the method of the present 10 invention. Such sensitive materials include low gauge polyethylene materials, low basis weight noawoveas and the like.
A substantial advantage of the present invention is that a 15 substantially continuous coating layers can be made from hot melts at very low coating weights. Bvea with customary commercially available hot melts, continuous layers can be produced at coating weights ranging from about 0.5 g/m= to as much.as 50-60 g/m', preferably at coating weights of not 20 more thaw about 30 g/m', more preferably at coating weights of not more thaw 20 g/m~, even more preferably between 10 g/ms and 20 g/ms and most preferably less than 10 g/m'.
However, coating weights higher than 60 g/m' may be useful for other applications wherein reducing the mechanical and 25 heat-induced stresses is of primary importance.
The very this coatings which can be produced according to the invention not only contribute to the economical advantages of the inventive method. but also makes it 30 possible to achieve a very much reduced stiffness of the material, which thus comes much closer, is its properties, to uncoated substrates.
35 The thenaoplastic cea~positioa As previously mentioned various thermoplastic materials may be used in the present invention such as various thermoplastic polymers may be used including polyethylene, wo ~nsoas PCT/EP98/o1588 -.
m 5 polypropylene, copolymers of olefins, especially ethylene, and (meth-) acrylic acid; copolymers of olefins. especially ethylene, and (meth-) acrylic acid derivatives, especially (meth-) acrylic acid esters; copolymers of olefins.
especially ethylene, sad viaylic compounds. especially vinyl 10 carboxylates such as vinyl acetates thermoplastic rubbers (or synthetic rubbers) such as styrene-isoprene-styrene, styrene-butadiene-styrene, styrene-ethylene/butylene-styrene sad styrene-ethylane/propylene-styrene block copolymers available in coerce under the tradeaames of lCratoa~, 15 Solprene~, and Stereon~; metallocene-catalyzed polymers, especially based oa ethylene and/or propylene: polyolefias such as ethylene, polypropylene and amorphous polyolefias (atactic poly-alpha-olefins) such as Vestoplast~ 703 (Hula); polyesterss polyamides; ioaomers sad corresponding 20 copolymers; and mixtures thereof. Such thermoplastic materials may be employed fa the coating method of the present invention uacompouaded provided the thermoplastic material is sufficiently low enough 3n viscosity. However, hot melt adhesives are preferred due to the ability to 25 independently tailor the viscoelastic properties, open time, tack, and various other properties. Hot melt adhesives commonly have melt flow indices required for such processing already at very low temperatures. Typical hot melts are fluid enough for such processing at temperatures ranging 30 from about 60°C to about 175°C. Additionally. various known hot melt moisture cure compositions are contemplated for use is the present invention.
With suitable hot melts, such as those described in DE-A-41 35 21 716, it is also possible to make materials which are impermeable to liquid water, yet water vapor permeable rendering the coating "breathable".

wo r~nsoas Pcr~~soisss is 5 In addition to commonly known hot melt adhesives, thermoplastic compositions compriaiag a water soluble, saline (body fluid) insoluble polymer such as Eastman AQ
copolyesters, commercially available from Eastman, are also particularly useful for creating barrier filans that are 10 impervious to body fluid, yet readily water soluble. This fsature is of particular interest for creating flushsble and compostable disposable hygienic products. Furthermore, thers may be applications wherein water permsability is desired. Accordingly, this coating method may also be 15 suitable for coating water soluble and/or biodegradable thermoplastic materials.
In the ease of the lamination adhesives for transparent substrates, thermoplastic polymers comprising substantially 20 or consisting entirely of one or more ethylene/methylacrylate copolymers ($MA's) and/or ethylene/n-butyl acrylste copolymers (BaBA's) is preferred.
EaBA copolymers are presently the most preferred such polymers.
More preferably, the thermoplastic composition exhibits certain rheological characteristics such that a substantially continuous coating can be produced at coating weights of less than about 50-60 g/m' and preferably less 30 thaw about 30 g/ms. In general, the rheological properties preferably fall within a rheological window wherein the complex viscosity at the coating temperature at high shear rates (1,000 rad/sec) is less than about 500 poise and the complex viscosity at low shear rates (< 1 rad/sec) is less 35 than about 1,000 poise. In other words, preferable thermoplastic compositions exhibit Newtonian regions at low shear rates and shear thinning at higher shear rates.
Thermoplastic compositions having wide windows of application are those in which the composition exhibits the WO 99/28048 PCT/EP98/01588 ._ 5 appropriate rheological properties at a variety of application settings. particularly law application temperatures. Narrow application windows are those fa which the rheological parameters are only met under very specific conditions.
The applicants surmise the complex viscosity sad high shear relates to the processing conditions at the slot die exit.
A composition with too high of a complex viscosity at 1,000 radiaas/sec would require excessive pump pressure to exit 15 the coating device. A die with a shim gap larger than 3 mm could be used to process these materials but a higher costing weight may result.
The comaplex viscosity and low shear relates to the settling of the coating on the substrate during the time it is suspended above the substrate. If the low shear value is too high, the coating may not adhere adequately to the substrate and/or the thermoplastic composition builds up at the nozzle causing a streaked. discontinuous coating. If the low shear viscosity is too low, the coating may seep into the substrate, causing poor barrier properties.
Extensioaal viscosity, which was not measured can also strongly influence the melt strength. Higher levels of 30 branching or the addition of s small concentration of a high molecular weight material can strongly influence the melt strength. More preferred, are compositions that meet the target rheological parameters at low application temperatures, less than about 177°G, preferably less than about 160°C. more preferably less than about 140°C, even more preferably less than about 125°C. most preferably less than about 110°C.

5 Aecordiagiy, many known hot melt adhesive compositions are well suited for use in the coating method of this invention.
Hot melt adhesives typically comprise at least one thermoplastic polymer, at least one plasticizer and at least one tackifyiag resin. Preferably, such suitable hot melts 10 comprise up to 50% by weight of thermoplastic polymer, up to 40% by weight of a plaeticizer sad up to 70% by weight of tackifying resin. In the case of hot melt adhesives which are not pressure sensitive, wax is generally employed is concentrations up to about 30% by weight of the adhesive.
Generally, the invention's hot melts will additionally contain one or more tackifyiag resins, plasticizers or oils and waxes plus customary additives and adjutants such as stabilizers, antioxidants. pigments, UV' stabilizers or absorbers, fillers etc. Plasticizera sad tackifying resins used in hot melt adhesives are known.
Oils such as naphthenic oils are preferred plasticizers. As for tackifying resins, those resins already knows for such 25 purposes are generally suitable, especially aliphatic, cycloaliphatic and/or aromatic hydrocarbon resins, ester resins and other such compatible resins. It is presently preferred to use either aliphatic or aromatic modified hydrocarbons resin. The preferred aliphatic resins are hydrogenated aliphatic hydrocarbon resin, for example, the EscorezC~ 5000 series available from the Exxon Chemical Co.
in Houston, TX and the Arkoa~ P sad M aeries available from Arakawa Chemical Co. and the Regalite~ series available from Hercules Inc. in Wilmington, DE. Roaias and rosin ester resins are also useful in the present invention. One such hydrogenated rosier acid tackifying resin is Foral~ AX
available from Hercules. Modified hydrocarbon resins such as modified terpenes including styrenated terpeaes such as 5 the Zonstsc~ series available from Arizona Chemical Co. in Panama City, FL sad the Kristalex~ series of alpha-methyl styrene resins available from Hercules, Inc. sad the Urataek~ series available from Arizona Chemical are also useful in the present invention. The components are mixed 10 and processed in a known manner to prepare the hot melts which can be used according to this invention.
Taxes are also useful is the present invention. These include synthetic high melting point waxes such as Fischer 15 Tropsch waxes available from Sasol (South Africa) under the tradeaame of Parafliat~, or from Shell Malaysia under the tradename Petrolite, and high density low molecular weight polyethylene waxes available from Marcus Chemical Co. under the tradeaame of Marcus~. AC S is another useful 20 polyethylene wax available from Allied Chemical.
Microcrystalliae waxes sad paraffin waxes are also useful to the present invention.
Laminating adhesives will preferably comprise up to 100% of 25 at least one thermoplastic polymer described above; 0-50% of an aliphatic hydrocarbon resin; 0-20% of as aromatic hydrocarbon resin; 0-40% rosin and 0-ZO% wax, said components sad their amounts being chosen so that the adhesive is in-lice coatable onto a laminating material 30 and/or a laminating substrate, for subsequent in-lice lamination of said laminating material to said substrate.
More preferably, is the case of film laminating, the adhesive will comprise the following components: up to 100%
35 of at least one EMA and/or EnHA copolymer; 0-50%
hydrogenated aliphatic hydrocarbon resin; 0-20% alpha-methyl styrene resin; 0-40% hydrogenated rosin and 0-20%
polyethylene wax.

5 The hot melt adhesive usable for practicing the invention s method can, in the simplest case, consist substantially or eves completely of one or more grades of EMA or EnBA
copolymers. ENA and EnHA copolymers are available from Elf Atochem under the Lotryl~ tradename, from Quantum Cheiaical 10 Co. sad From Exxon Chemical Co. under the Optemta~
tradename. A variety of different grades of BMA sad EaHA
copolymers are available. They mainly differ in eater content, melt flow index (MFI) and melting point.
15 In presently preferred special embodiments, the hot melt adhesive essentially consists of 35-60% EaHA or EMA; 30-50%
hydrogenated aliphatic hydrocarbon resin or about 10% alpha-methyl styrene resin= 0-30% hydrogenated rosin and 0-10%
polyethylene wax, plus small amounts of stabilizer. In some 20 preferred embodiments, the thermoplastic polymer of the hot melt adhesive is a single grade of EnBA copolymer, usually at the low end of the MFI range (i.e. MFI less than 10 g/10 min.)In other preferred embodiments, the thermoplastic polymer comprises more than one grade of EnBA, and in these 25 cases, two or three different grades wherein at least two of the grades preferably have MFI~s whioh differ by at least s factor of 4 and up to a factor of 10 (i.e. one grade has an MFI more thaw 4 times that of the other grade.
30 The inventive hot melts can be used at application temperatures (or processing temperatures) which are law enough to prevent distortion of heat sensitive plastic film, and at the same time show excellent flow properties at such low temperature. It is, for example, possible to coat and 35 laminate the inventive hot melt on the laminating materials.
Non-contact coating is especially advantageous for heat sensitive films. Excellent film forming performance a.s achieved, and the laminated products exhibits high glossiness.

The laminating adhesives of the invention produce high transparency of the hot melt coating, so that high gloss is achieved, while readability and color rendition of, for example, printing oa tha substrate is not impaired.

The inventive hot melts show excellent (high) hot-tack and open time characteristics for the method of the present invention as well as setting properties. They meet the requirements of machine condition, ia-line embossing and 15 cutting, for example, is the graphic arts industry.
Laminates made according to the invention exhibit high heat resistance and high W resistance, and correspondingly little delaminatioa or yellowing. Also after heat forming 20 and embossing, no delamiaatioa is observed whey the hot melt formulations of the invention are used.
The following non-limiting examples further assist is illustrating the present invention.

Sot melt adhesives were produced from different 30 thermoplastic polymers, tsckifiers and plastizisers as shown in Table 1 below:

r ~ ~ , , , , , , , ~ , , , ~ , O th N1 I~f1 ~ O ~ ~ ,t1 w s~ ~ ~ a ~ a o ~ , o a ~ ~ a ~' a ~, b .

~ ~ o >. ~u>. ~ ~ w ~ a ~ m s~

~ o ~ g, x .a.xs..~ a a a ~ s o r ~ 4~

..ia ~ o .ao a ,~a w G a ~ a o ~. a ~. a o ~ ,tee.~ m .~a ~ ~ ~

a o~v ~ ~~ w ~ w u w m ..~r~.
d ~ w w o ~'' w d a ~ o ~ a, w e x s ~ u m a , 5 Sot melt adhesives corresponding to the compositions depicted in Examples l and 7 were coated onto substrates, using a modified PAR 600 laminating machine by Rroenert, Hamburg, Germany. The structure of this machine is basically similar to that shows in Fig. 1B. With this type 10 of machine, it is possible to nip the adhesive film directly onto the first substrate (1) by means of nip roller (5) or nip a second substrate (4) onto the first substrate and adhesive, again by means of nip roller (5). In the tests, both methods were tried. The dispensing temperature of the 15 hot melt was 140°C for the composition of Example 1, and 110°C for the composition of Example 7. These compositions show favourable low viscosities, as is notable from the diagram Fig. I4. 'This diagram illustrates the viscosities of Examples 1 and 7.
Coatings were made on polyester film (Polyester RN 36, produced by Piitz Folien, Taunusstein-Wehen, Germany) and high density polyethylene films (HDPE RC 3664.00, obtained from Mildenberger + Willing, Gronau, Germany).
As a second substrate (where used), these films were also used. In other experiments, silicone paper was used instead.
Tests were also made with printing paper sheets as the second substrate.
Coating weights were 5 to 6 g/mz at machine speeds of approximately 70 m/minute.
The adhesive film was released from the coating slot nozzle, at various distances from the first substrate (1) to be coated with the adhesive, in a variety of tests. In another set of experiments. with a vertical configuration (similar to Figs. 3-5, 7, 9 and 10) it was found that the distance of the slot nozzle from the substrate could be varied between a SUBSTITUTE SHEET (RULE 26) WO 99/2804$ PCT/EP98/01588 few millimeters and up to 500 mm and more, without materially affecting the quality of the coating.
Wherein these experiments, the adhesivs filan releaaed from the coating slot nozzle was directly coated onto the first 10 substrate by mesas of nip roller (5) provided with a release coating, it was found that the adhesive did not adhere to the nip roller. The nip presaure was not measured, but the nip roller was pressed against the substrate at a laminating pressure of 7 to 8 bar.
It was found that the adhesive coated onto the first substrate left the nip station with no air enclosed between the adhesive sad the first substrate.
20 In other teats, a second substrate was laminated onto the adhesive layer by a second set of rollers, located is the flow path of the substrate upstream of the nip roller (5).
Also these laminations, using the same films, or release-coated paper. as above discussed, were examined for streaking, enclosed air, or other lamination defects.
The laminations thus made were all free of flaws. No streaking, enclosed air or any other defects were observed.
30 Ia a similar fashion, laminations were made using the same type of films, but the other adhesives depicted in Examples 2 to 6 of Table 1. The results were as good as those obtained with the adhesive compositions of 8xamples 1 and 7.

Claims (28)

1. A method of coating, wherein a hot melt adhesive, which has been thermally made flowable, is released from a coating device onto a substantially nonporous substrate as a substantially continuous coating without contact between said coating device sad said substrate, and subsequently disposed upon the surface of said substrate.

2. A method of coating, wherein a hot melt adhesive, which has bees thermally made flowable, is released from a coating device onto a substrate as a substantially continuous coating without contact between said coating device and said substrate, and subsequently disposed upon the surface of said substrate, wherein the distance between the coating device and the substrate is greater than 20 mm.

3. A method of costing, wherein a hot melt adhesive, which has been thermally made flowable, is provided in the form of a substantially continuous nonporous film without contact of the film with a substrate or a roller, and said film is then coated onto s substrate by means of a release-coated roller is direct contact with the adhesive film, said roller nipping said adhesive sad said substrate.

4. A method of coating, wherein a hot melt adhesive, which has been thermally made flowable, is released from a coating device onto a release coated roller as a substantially continuous costing without contact between said coating device sad said roller, sad subsequently disposed upon the surface of a substrate.

5. A method of coating, wherein a hot melt adhesive, which has been thermally made flowable, is provided is the form of a substantially continuous nonporous film without contact of the film with a substrate, and said film is then coated onto a first substrate, with a release-coated substrate disposed upon that surface of the hot melt adhesive which is not is contact with the first substrate.

6. A method of coating, wherein a hot melt adhesive, which has been thermally made flowable, is provided is the form of a substantially continuous nonporous film without contact of the film with a substrate, and said film is then disposed upon a release-coated substrate and is then transfer-coated onto a second substrate.

7. A method of coating, wherein a hot melt adhesive, which has been thermally made flowable, is released from a coating device onto a first substrate as a substantially continuous coating without contact between said coating device sad said first substrate, and subsequently disposed upon the surface of said first substrate, wherein said coating is reheated and then contacted to a second substrate.

8. A method of coating, wherein a thermoplastic material which has been thermally made flowable, is provided in the form of a substantially continuous nonporous film without contact of the film with a substrate and said film is then coated onto a substantially nonporous substrate.

9. A method of coating, wherein a thermoplastic material, which has been thermally made flowable, is released from a coating device at less than about 240°C in the form of a substantially continuous nonporous film, without contact of the film with a substrate, and said film is then coated onto a substrate.

10. A method of coating, wherein a thermoplastic material, which has been thermally made flowable, is provided in the form of a substantially continuous nonporous film without contact of the film with a substrate and said film is then coated onto a substrate, said coating having a complex viscosity of less than about 500 poise at about 1000 radians/sec at the coating temperature.

11. A method of coating, wherein a thermoplastic coating having a complex viscosity of less than about 500 poise at about 1000 radians/sec at the coating temperature has been thermally made flowable is released from a coating device onto a nonporous substrate as a substantially continuous coating without contact between said coating device and said substrate, sad subsequently disposed upon the surface of said substrate.

12. A method of coating, wherein a thermoplastic coating having a complex viscosity of less than about 500 poise at about 1000 radians/sec at the coating temperature, which has been thermally made flowable, is released from a coating device onto a substrate as a substantially continuous coating without contact between said coating device and said substrate. and subsequently disposed upon the surface of said substrate, wherein the distance between the coating device and the substrate is greater than 20 mm.

13. A method of coating, wherein a thermoplastic coating having a complex viscosity of less than about 500 poise at about 1000 radians/sec at the coating temperature, which has been thermally made flowable, is released from a coating device onto a first substrate as a substantially continuous coating without contact between said coating device and said first substrate, and subseguently disposed upon the surface of said first substrate, wherein said coating is reheated and then contacted to a second substrate.

14. A method of coating, wherein a thermoplastic coating having a complex viscosity of less than about 500 poise at about 1000 radians/sec at the coating temperature, which has been thermally made flowable, is released from a coating device onto a release coated roller as a substantially continuous coating without contact between said coating device sad said roller and subsequently disposed upon the surface of a substrate.

15. The method of claims 8 to 14, wherein said thermoplastic coating has a complex viscosity of less than 1000 poise at about 1 radians/sec at the coating temperature.

16. The method of claims 1 to 15, wherein said substrate is selected from the group consisting of film, foil, paper and combinations thereof.

17. The method of claim 16, wherein said first and said second substrates are selected from films, foils, paper, coated paper, co-extruded films and other laminating materials, and said adhesive is a nonreactive adhesive, or a reactive hot melt adhesive.

18. The method of claims 15 or 16, wherein said coated substrate comprises a heat sealing material.

19. The method of claims 1 to 18. wherein said coating device is a slot nozzle.

20. The method of claims 1 to 19, wherein said coating has an area weight of less than about 60 g/m2.

21. The method of claims 1 to 20, wherein the coating has as area weight of less thaw about 30 g/m2.

22. The method of claims 1 to 21, wherein the coating has an area weight of less than about 10 g/m2.

23. The method of claims 8 to 14, wherein the thermoplastic composition is released from the coating device at a temperature of less than about 160°C.

24. The method of claims 8 to 14, wherein the thermoplastic composition is released from the coating device at a temperature of less than about 110°C.

25. The method of claims 1 to 24, wherein a first substrate is bonded to at least one second substrate ,,inline" or ,,offline".

26. The method of claims 1 to 25, wherein the distance between the coating device and the substrate ranges from about 0.5 mm to 500 mm.

27. A book cover made by any one of the methods of claim 1 to 26.

28. A lamination made by any one of the methods of claims 1 to 26.