GB2284381A - Method of forming a reactive polymer system - Google Patents

Abstract

An apparatus far forming a polymer system (1) from at least two separate reactive components includes a pair of reactant storage vessels connected to respectively a first reactant application means (15) for depositing a reactive component as a film over a substrate (19); and a second reactant application means (17) arranged to deposit the second reactant as a film over the first reactant to form a reactive polymer system. The second reactant may be applied as a film over a second substrate 21 or contacted, while supported by that substrate, with the first reactant supported on first substrate 19, for example by passing through nips between roll pairs 27, 29; 31a, 33a and 31b, 33b after which one or both substrates can be removed. The apparatus may be used to produce, for example, oligomers for continued reaction at a later time or for inclusion in a further reaction process, or a desired completed polymeric material, which may be placed either onto or between the substrate or substrates to act as either an adhesive, surface coating or core of a laminated material or a combination of such. <IMAGE>

Description

Method of forming a reactive polymer system The present invention relates to a method and apparatus for forming a reactive polymer system, and more especially but not exclusively to a method and apparatus for the formation of thin sheet or film from a reactive two component polymer system.

The thermoset class of polymers and some thermoplastic polymers are synthesised in two stages. Firstly a combination of reactive monomers are made to oligomerise to produce an oligomer or resin which has reactive chemical sites on its short polymer-chain molecules. Secondly the oligomer is reacted with another oligomeric or monomeric material under carefully controlled conditions to produce either a thermoplastic or thermoset material. The present invention is applicable to the formation either of the oligomer or the second reaction product Conventionally, commercial processing methods for the production of polymeric products from a dual component reactive polymer system involve preconditioning by controlling the temperature and dispersion of additives within storage tanks holding the components. The components are then pumped from their respective tanks.The ratio of the quantity of each component delivered by the pumps must be accurately controlled to equal the required stoichiometric ratio of the reactive system, and is normally carried out through metering the volume of each component delivered and subsequently calculating the mass output from a knowledge of the component's density, which will, of course, vary with temperature. The accuracy of such a calculation depends on many environmental and physical factors so that the quality of the polymer will tend to worsen as the delivery and metering system deteriorates with age. The final stage in the process is to mix the ingredients thoroughly and this can be carried out by stirring the mixture either with a mechanical element or by letting streams of each component impinge on a series of static vanes, within a mix chamber.In each case the mix chamber must be flushed between batches of production.

Another commonly used technique is to direct the streams at high velocity towards each other within a mix chamber so that high velocity impingement and turbulent mixing occurs. A variation of this technique involves arranging the streams to issue one above the other so that the upper stream moves downwards to meet the lower stream and thus mix. Normally the mix chamber is cleaned between each batch of production by passing a hydraulically operated ram through the chamber.

According to the invention there is provided a method of forming a polymer system from at least two separate reactive components including the steps of: continuously applying a film of a first reactive component on to a substrate; and continuously bringing the film of the first component into contact with a film of a second reactive component; whereby the contacted films form a reactive polymer system.

Such a method may be used to produce, for example; i) Oligomers for continued reaction at a later time or included in a further reaction process.

ii) A desired completed polymeric material which has been placed either onto or between a substrate or substrates and acts as either an adhesive, surface coating or core of a laminated material or a combination of such.

Thus, the second component may also be applied to a second substrate in the form of a film before the films are brought into contact by causing the substrates to approach one another, or the second film may be applied, for example by extrusion, directly over the first. The reactive components may be allowed to cure while they remain on the substrate or substrates, to form a cured layer of polymer, and one or both substrates may then be stripped from the polymer layer to leave the latter as a coating or a self-supporting film.

Alternatively the reactive polymer system may be removed from the substrate or substrates prior to curing, to provide an oligomer or a mixed two component system as a mass of material for use, for example, in a moulding process.

The invention takes advantage of the applicants' observation that polymerisation or oligomerisation at an interphase between layers of a two component system is effective to promote a reaction throughout the two layers, provided the layer thickness is not above a certain value, without a requirement for further mixing and takes advantage of the fact that reactions can be considerably better controlled in thin films than in bulk phases with large crosssection where uniform and rapid heat transfer and homogenous mixing to a sufficient level for diffusion and consequent molecular reaction to occur is difficult to obtain. The value of the film thickness will vary according to the specific materials being reacted and thus would have a working range and an optimum value. The value would be influenced but not limited to such factors as surface tension, viscosity, surface energy etc.For example, a value for Urethane using typical MDI or TDI and polyols with viscosities at a process temperature in the order of 300 to lOOOcps, would be approximately 100 microns. Specific easy to mix systems have shown success at the 250 micron range. There would not be a minimum value for successful mixing however the economics of the product would be a factor. The invention is therefore particularly advantageous and convenient when applied to the oligomerisation of very fast reacting low molecular weight polyamines, which tend to form non-uniform gels when oligomerised by conventional bulk methods.

Thus numerous disadvantages inherent in the known mixing processes may be overcome.

Advantageously, the ratio of film thickness is controlled to provide the required chemical ratio of the reactants.

Conveniently the film thickness ratio may be varied from a strict stoichiometric ratio in order to produce oligomers of specific molecular weight and functional grouping.

The contacted films may be heated or cooled to increase or decrease the rate of reaction of the polymer. Additionally the substrate and/or environment may be temperature controlled to further alter the rate of reaction.

According to a further aspect of the invention there is provided an apparatus for forming a polymer system from at least two separate reactive components including; a pair of reactant storage vessels connected to respectively; a first reactant application means for depositing a reactive component as a film over a substrate; and a second reactant application means; whereby the second reactant application means is arranged to deposit the second reactant as a film over the first reactant to form a reactive polymer system.

Advantageously the apparatus includes means for controlling the thickness of the film of each reactive component such that components are produced in the correct stoichiometric ratio to produce a consistent product.

In order to aid in understanding the invention a specific embodiment thereof will now be described by way of example, and with reference to the accompanying drawings, in which: Figure 1 is a block diagram of an apparatus for mixing reactive materials according to the invention; Figure 2 is a perspective view with its support framework omitted for clarity of the substrate coating and contacting section of the apparatus of Figure 1; Figure 3 is a similar view of a substrate removal section of the apparatus of Figure 2; Figure 4 is a similar view of a variant of the substrate removal section of Figure 2.

Figure 5 is a schematic block diagram of a further embodiment of the invention; Figure 6 is an enlarged sectional side view of a dispersion block of the apparatus of Figure 5 on the line VI VI of Figure 7; and Figure 7 is a sectional end elevation of the dispersion block on the line VII-VII of Figure 6.

Referring to Figures 1 to 3 of the drawings, an apparatus for forming a reactive polymer system 1, which may be understood to include the formation of oligomeric as well as polymeric products, has a substrate coating section 3 located upstream of a coated substrate contacting section 5, which precedes an oven 7. A substrate removal and product retrieval section 9 is positioned downstream of the oven 7.

The substrate coating section 3 has first and second substrate roll carriers 11,13. A reactive component delivery spurge bar 15,17 is situated downstream of each carrier 11,13 and provides reactant from a storage vessel (not shown). A guide roller 18 reverses and inverts coated substrate 19 from the first carrier 11 so that it travels with the same sense of direction as the coated substrate 21 provided by the second lower carrier 13, for introduction to the contacting section 5.

Both coated substrates 19,21 are brought into abutment along their respective coated surfaces 23,25 by passing each substrate into the nip 35 of a pair of horizontally arranged, vertically separated, guide rollers 27,29. A further pair of horizontally arranged, vertically separated, guide rollers 31a,33a have a nip 37 and subsequent pairs 31b,33b as necessary for substrate or cure type cycle, sufficient to kiss the abutting coated surfaces 23,25 into pressing engagement before the substrate and reactant laminate is heated in the oven 7 to facilitate the polymerisation of the reactants.

The substrate removal and product retrieval section 9 has a pair of stripper rollers 39,41 the first of which removes the upper substrate 19 and the second 41 the lower substrate 21 to leave an unsupported film of polymerised material 43 which may be cut to length as required.

In a variant of the invention, shown in Figure 4, reactants may be chosen which form an oligomer product. Nonreactive metal foil substrates are used in order that the oligomer product may easily be stripped from the supporting substrates by upper and lower stripping knives 45,47 and the substrates subsequently reclaimed.

In a further non illustrated variant, one of the substrates only is removed to produce a surface-coated product.

In use, care must be taken to ensure that the liquid reactants wet and spread across the substrate materials, to control uniform film thickness and hence reaction ratio. This may be a problem with some plastic materials substrates having lower surface free energy than either of the liquid reactants.

Spreading may be encouraged through the use of viscosity and surface tension modifiers contained in the reactants.

It will be appreciated that the invention may also be employed to produce other sheet and film products.

For instance, adhesive, being a thin film, may be applied to continuous and flat substrate which has a good surface smoothness and low porosity. Hence laminated products may be produced by applying an adhesive between the contacting surfaces of each substrate or the adhesive may be applied to a pair of substrates, one of which is a release film, the release film may then subsequently be removed to leave an adhesive coated substrate. This technique may also be used to prepare surface coated sheet and film products. A polished or leather grain effect surface finish may be achieved, in the case of unsupported or surface coated films, by using suitably textured release film.

Figures 5 to 7 show a further embodiment of the invention in which a pair of optionally temperature controlled, reactant storage vessels 101,103 provide the reactant supply for a pair of separate delivery and recirculation circuits 105,107.

Reactant 109,111 from the vessel 101,103 is gravity or pressure fed, via a heat exchanger 110,112, to a gear or other suitable type pump 113,115 which is driven by a speed controlled device such as an electric motor 117,119 to pump each reactant at a pressure of around 50 to 100 psi. A pressure transducer 121,123 and safety valve 125,127 are situated in the delivery circuit 105,107 downstream of the pump 113,115. A flowmeter 129,131 provides an output to enable control, by means of the variable speed control of the motors 117,119, or by direct adjustment of the pump output, of the ratio of the reactants 109,111. Two three-way mechanically simultaneously operated valves 133,135 allows reactant to be recirculated to the vessel 101,103 or directed to an inlet nipple 137,139 of a dispersion block 150.

Separate streams 140,141 of reactant 109,111 issue from the block 150 onto a temperature controlled lay down drum 143 so that the first stream 140 is laid on the drum's surface 145 and the second stream is deposited as a film over the reactant 109 film coating the drum 143. The rotational speed of the drum 143 being controlled by any conventional method such as frequency drives, variable pulleys, gears or such like mechanism in order to control the thickness of the films. A doctor blade 147 optionally scrapes the polymerised product from the surface 145 of the drum to fall into a collection vessel 149 or conveyor type system into a post cure or temperature controlled area (not shown).

In a non-illustrated variant of the invention shown in Figures 5 to 7, the two three-way mechanically simultaneously operated valves are replaced by four two-way valves.

In more detail, the dispersion block 150 has a manifold 151,153 connected to each nipple 137,139 and leading to a chamber 155,157. The chamber 155,157 reduces in cross-section to an exit slit 159,161. The width of the slit 159,161 is adjustable by means of a plate 163,165 slidingly mounted on the underside of the block 150 by a fastening mechanism (not shown). In use, the width of the slit is set by releasing the fastener and adjusting the slit 159,161 by suitable means such as a micrometer type mechanism attached to the plate 163,165 or by simply by inserting a feeler gauge (not shown) into the slit 159,161 and locking in places with the fastener mechanism.

In use, the apparatus may be employed to apply two-pack reactive coatings and thin film adhesives to substrates, for example to manufacture laminated goods, in which case the heated drum may be replaced by a conveyor or the like, carrying the substrate to be coated. A further use may be in moulding where slower reacting dual component systems produced by the apparatus can be dispensed into a mould cavity with minimal air incorporation into the mixture.

Claims (17)

Claims

1. A method of forming a polymer system from at least two separate reactive components including the steps of: continuously applying a film of a first reactive component on to a substrate; and continuously bringing the film of the first component into contact with a film of a second reactive component; whereby the contacted films form a reactive polymer system.

2. A method according to Claim 1, including the step of further reacting the reactive polymer system at a later time.

3. A method according to Claim 1 or 2, wherein the formation of the reactive polymer system provides a step in a further reaction process.

4. A method according to any one of Claims 1 to 3, including the step of applying the film of the second component to a second substrate before the films are brought into contact by causing the substrates to approach one another,

5. A method according to any one of Claims 1 to 4, wherein the second film is applied, by extrusion, directly over the first.

6. A method according to any preceding Claim, wherein reactive polymer system is applied onto or between the substrate or substrates and acts as either an adhesive, surface coating or core of a laminated material or a combination of such

7. A method according to any one of Claims 1 to 5, wherein the reactive components are allowed to cure while they remain on the substrate or substrates, to form a cured layer of polymer, and one or both substrates may then be stripped from the polymer layer to leave the latter as a coating or a self-supporting film.

8. A method according to any one of Claims 1 to 5, wherein the reactive polymer system is removed from the substrate or substrates prior to curing, to provide an oligomer or a mixed two component system as a mass of material for use in a moulding process.

9. A method according to any preceding Claim, wherein the ratio of film thickness is controlled to provide the required chemical ratio of the reactants.

10. A method according to any one of Claims 1 to 6 or 8 to 9, wherein the film thickness ratio is varied from a strict stoichiometric ratio in order to produce oligomers of specific molecular weight and functional grouping.

11. A method according to any preceding Claim, wherein the contacted films are heated or cooled to increase or decrease the rate of reaction of the polymer.

12. A method according to Claim 11 wherein the substrate and/or environment is temperature controlled to further alter the rate of reaction.

13. A method as claimed in claim 1, substantially as described herein.

14. An apparatus for forming a polymer system from at least two separate reactive components including; a pair of reactant storage vessels connected to respectively; a first reactant application means for depositing a reactive component as a film over a substrate; and a second reactant application means; whereby the second reactant application means is arranged to deposit the second reactant as a film over the first reactant to form a reactive polymer system.

15. An apparatus according to Claim 14, wherein means are provided for controlling the thickness of the film of each reactive component such that components are produced in the correct stoichiometric ratio to produce a consistent product.

16. An apparatus according to Claim 14, arranged to carry out the method of any one of Claims 1 to 12.

17. An apparatus substantially as described herein.