Technical Field

The invention relates to acrylate prepolymers compositions, acrylate polymer gels and polymer compositions derived therefrom, and to processes for the preparation of these compositions. The invention also relates to articles manufactured from the acrylate polymer gels and polymer compositions and to processes for the manufacture thereof.

Background Art

Corrugated sheets of fibreglass reinforced polyester are commonly used in building applications, because they are relatively inexpensive, readily available, and convenient as light-transmitting panels. However, such polyester sheets do not have good outdoor environmental stability, being affected by ultraviolet light and erosion. Ultraviolet light causes crazing and an increase in opacity, adversely affecting the light-transmitting properties of such panels, whereas environmental erosion of the polymeric matrix exposes the fibreglass reinforcing material.

Clear building panels based on polycarbonate have a much higher degree of outdoor environmental stability, but the cost is very expensive compared to polyester, the cost being prohibitive for most large-scale commercial and Industrial applications, such as greenhouse construction.

An alternative, economical starting material is an acrylate monomer. Acrylate monomers such as methvlmethacrylate ⁽ MMA) monomers are unstable at a pient conditions and therefore they have to be stabilised. Before such monomers can be polymerized the stabiliser has to be extracted. This is an expensive and time consuming process. Further, on extraction of the stabiliser the acrylate monomer is highly active and must be converted into a product immediately. A further disadvantage is that the monomer shrinks up to 30% during polymerisation.

In the present invention extraction of the stabiliser is not necessary. The polymerization of the stabilized monomer is achieved directly.

Description of the Invention

According to a first embodiment of this invention, there is provided an acrylate prepolymer characterised in that it is derived from a stabilised acrylic monomer which is polymerised in the presence of the stabilisers to a degree such that it is of a vise sity suitable for moulding and is readily polymerised by the application of UV light, heat or other radiation.

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According to a second embodiment of this invention there is provided a process for the preparation of an acrylate prepoly er which process comprises heating a mixture of a stabilized • crylate monomer together with an initiator to between 70° and 87°C to polymerize the mixture until the viscosity of the mixture reaches a selected viscosity, and then cooling the mixture to substantially terminate polymerization to provide the prepolymer, wherein the initiator is maintained at greater than 1/2 the amount initially supplied.

Typically the selected heating is at between 70°C and 85°C. The selected viscosity may be between 30 and 500 poise, typically the viscosity depends on end use of the prepolymer. During final polymerisation, there is less than 1% shrinkage.

Acrylate monomers suitable for use in the preparation of the acrylate prepolymer include esters of methacrylic and acrylic acid such as methyl, ethyl, butyl, isobutyl, 2-ethylhexyl , lauryl, stearyl , 2-hydroxyethyl , 2-ethoxyethyl , 2-hydroxypropyl , 2-dimethylaminoethyl and t-butyl a ino ethyl esters and derivatives thereof and anhydrides, chlorides and amides of acrylate and methacrylate.

Plasticisers or other viscosity modifying agents and/or other additives may be added to the acrylate monomer before formation of the prepolymer.

In this specification, the term "plasticiser" in addition to conventional plasticisers includes substances capable of modifying the hardness and/or elasticity of the polymeric articles of the invention. Such substances include epoxys (without catalysts), PVC and its copolymers.

Alternatively, a prepolymer of low viscosity, suitable for blending additives, can be formed, the additives blended with the prepolymer and then prepolymerisation continued until the desired viscosity is achieved.

Further, prepolymer mixed with plasticiser can be used as a modifying agent in a prepolymer.

Preferably the initiator is a peroxide, more preferably, benzoyl peroxide.

The invention also provides, in a third embodiment, acrylate polymer gels which comprise the prepolymers of the invention optionally combined with gel-forming amounts of UV initiators and/or plasticisers and/or viscosity modifying agents and/or other additives and which have been formed into gels by the action of heat or UV radiation.

In a fourth embodiment of this invention there is provided a process for the preparation of an acrylate polymer gel which process comprises optionally blending acrylate prepolymer with an additive

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and/or with a gel-forming amount of a UV initiator and partially or fully polymerising the mixture to form the acrylate polymer gel . The mixture may be partially or fully polymerised by the application of heat or UV radiation. The compositions comprising additives can be formed by blending the prepolymer optionally combined with a UV initiator with the additives or by forming the prepolymer in the presence of the additives.

Preferably the UV initiator is 0.005-5 wt%, typically 0.1 wt% benzyl dimethyl ketal .

Preferably the plasticiser is butyl phthalate.

In a fifth embodiment of the invention there is provided a first polymer composition comprising the prepolymer of the Invention and optionally plasticisers and/or viscosity modifying agents and/or other additives. Such compositions can be formed by blending the prepolymer with other additives or by forming the prepolymer in the presence of those additives.

In a sixth embodiment, there is provided a second polymer composition comprising the polymer gel of the invention and optionally plasticisers and/or viscosity modifying agents and/or other additives.

The invention provides, in a seventh embodiment, a third polymer composition comprising the prepolymer of the invention and the polymer gel of the invention and optionally plasticisers and/or viscosity modifying agents and/or other additives.

Typically, 5-70 ^* /. by weight of an acrylate polymer gel is blenαed with an acrylate prepolymer and a cross-linking agent at 0-25wt7.. Generally the acrylate polymer gel is present in the blend at 15-50 wt%. Preferably the cross-linking agent is glycidyl methyl methacrylate or trimethyl propane triethoxy triacrylate.

An eighth embodiment of the invention provides a process for the manufacture of polymeric articles which process comprises placing a polymer composition according to the invention into a mould and causing the prepolymer therein to polymerise.

UV radiation or heat may be used in polymerisation of the acrylate polymer gel and polymer compositions of the invention. It is preferred to use UV radiation in the polymerisation process, preferably either low level UV-B or sunlight. It is particularly preferred to employ UV radiation at 280 to 340nm of low power, eg, from 40W 1.2m fluorescent tubes.

When UV illumination is used in the polymerisation process , best control is maintained at ambient temperatures, although higher temperatures and pressures may be used for rapid polymerisation.

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An advantage of the process for the preparation of polymer gels and the polymer compositions according to the invention is that when UV radiation is used in the polymerisation procedure only a small amount of UV initiator is required (typically 0.1 wt% vs 1-2 wt7. in other UV polymerisation processes). As UV initiators are expensive this is a substantial economic advantage.

Further when the second, fourth and eighth embodiments are used in combination heat and UV formation and polymerisation steps can be used for the economical production of poly erics articles according to the invention.

Additives may also be incorporated into the blend.

In this specification the term "additive" may include glass fibres, dyes, pigments, reinforcing fibres and/or fillers. Reinforcing may be fibrous such as fibreglass, nylon, carbon fibre, woven fibre or Kevlar (Trademark), or non-fibrous such as clay, hydrated magnesium oxide or calcium carbonate. Surprisingly, fibres and fillers are readily wet by the prepolymer of the invention. Reinforcing fibres can be blended with the prepolymer before moulding or laid up in the moulds prior to addition of the prepolymer and polymer gel.

Colour which is generated during the formation of the prepolymer process as a result of breakdown of the stabilising systems and impurities is eliminated during final polymerization whereby the material becomes totally colourless and clear, comparable to glass. Sheets and panels produced according to the invention are ideal for use as light transmitting panels in greenhouses or other building structures.

Mixtures of prepolymer with plasticiser can be used as a modifying agent in a prepolymer. The relative ratios of modifying agent to prepolymer determines the flexibility or hardness of the end product. Such a modifying agent is most effectively used at prepolymer:modifying agent ratios of 1:2 to 1:6.

The acrylate polymer composition can be prepared in shaping baffles or in a mould to provide an article of desired shape.

Accordingly, a nineth embodiment of the invention provides polymeric articles produced by carrying out the eighth embodiment of the invention.

For forming sheeting the blend is placed between polyester films which are drawn through rollers. For profiled sheeting the blend may be drawn between film through a number of sets of profiled baffles conforming to the desired profile for the sheet and polymerised with UV illumination after each set. For shaped articles the acrylate polymer composition blend is introduced into a mould and polymerised.

Articles which can be manufactured from the polymer compositions according to the invention include a range of products from flexible membranes and sheets to rigid self-supporting structures. The polymer compositions of the invention can be used in like manner to conventional reaction-in-mould processes for production of similar articles.

Preferably the articles produced are corrugated or flat roof sheeting.

The viscosity or the degree of polymerisation of the prepolymer can be tailored specifically to the end product to be produced. For instance the degree of polymerisation required for sheet formation will differ from that required for reaction-in-mould applications. The acrylate resin can be readily modified by the addition of polymers such as PVA and PVC. Addition of such polymers will result in an increase in opacity proportional to a percentage of modifying resin used.

Addition of PVC in amounts of from about 1°/. to about 50% by weight gives beneficial properties in terms of the rigidity of the final product. The addition of PVC which has been pre-plastici sed together with acrylate produces good film forming or membrane forming characteristics. The PVC and the acrylate prepolymer combines to form a polymeric alloy.

Such a film can be cured very quickly at ambient temperatures or at elevated temperatures of up to 150°C.

Brief Description of the Drawing

Fig. 1 is a plot of temperature and viscosity against time for polymerisation of MMA monomer in the presence of benzoyl peroxide. Best Method and other Methods of Carrying out the Invention

Acrylate prepolymers of the invention may be prepared by heating stabilized methylmethacrylate monomer to 70-85°C, typically 75°C, to break down the stabilizer and cause partial polymerization and a consequent increase in viscosity in the monomer. The heating step is performed in the presence of an initiator, benzyl peroxide, which initiates polymerization. The heating should not be in excess of 87°C since uncontrollable polymerization occurs above this temperature. The viscosity of the prepolymer is monitored. When the viscosity is between 30 and 500 poise, typically 50 poise the prepolymer is cooled to room temperature. This terminates polymerization to yield a prepolymer in the form of a viscous 1 iquid.

Polymer compositions of the invention may be prepared by mixing the acrylate prepolymer with butyl phthalate and a UV initiator, benzyl dimethyl ketal . The UV initiator is used in an amount of about 0.1% by weight. UV illumination is applied to form a polymer gel.

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To form a polymer composition, the polymer gel may be blended with the prepolymer. The ratio of polymer gel to prepolymer is chosen depending on the type of polymer composition to be formed. The more polymer gel used, the softer the resulting polymer composition is. Typically 15-20% by weight of the blend is polymer gel. A cross-linking agent up to 5% by weight is added, namely, glycidyl methyl methacrylate. Other additives, especially glass fibres, are employed as required. The resulting polymer mix is exposed to UV illumination to cross-link the polymer into the polymer composition.

The above processes may be combined to form a continuous process for the production of a polymer composition from an acrylate monomer.

Typically, such a process comprises:

(a) heating a stabilized acrylate monomer to between 70° and 87°C to polymerize the monomer until the viscosity of the polymerizing monomer increases to between 30 and 500 poise and then cooling the polymerizing monomer to room temperature to terminate polymerization to provide a prepolymer;

(b) blending the prepolymer with butyl phthalate and exposing the blend to UV light to form a polymer gel; and

(c) blending 5-70% by weight of the polymer gel with the prepolymer, adding a cross-linking agent at 2-5% and exposing the mix to UV light.

In preferred forms of this process the ^" heating is between 70°C and 85°C, whereby said viscosity can increase to 500 poise. A UV initator, benzyl dimethyl ketal is added to the blend. The amount of polymer gel blended is 15-50 wt%. The cross-linking agent is glycidyl methyl methacrylate or trimethyl propane triethoxy triacrylate.

Additives may be incorporated into the blend as hereinbefore described.

Polymers articles according to the invention may be prepared by exposing the blend to UV illumination after it has been shaped in a mould or by baffles. The amount of UV illumination to which the. article is exposed is critical in the sense that an effective amount of UV illumination to polymerise the blend to completion must be used.

Polymer sheeting can be prepared by placing the polymer blend between polyester films and drawing it through shaping baffles and illumination with a UV light.

When shaped articles such as corrugated sheeting are required, a series of spaced baffles are used. The film clad polymer blend is shaped

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into a profiled sheet conforming to the profile of the baffles as it is drawn through the baffles and illuminated with UV after passing through each set of baffles. Laminates of flat or profiled sheeting, can be formed by layering polymer blend between alternate layers of polymer blend with glass fibres, all between polyester films.

Examples Example 1

A prepolymer was prepared by adding MMA monomer to a reactor vessel having heating and cooling facilities. Benzoyl peroxide was mixed into the MMA at a ratio of 160:1. The mixture was heated with continuous stirring as illustrated in Figure 1.

The resultant prepolymer was then used to form clear sheeting with good impact characteristics, as follows. Example 2

100 parts of pre-polymer having 60 sees viscosity was mixed with 150 parts di-butyl phthalate and 50 parts di-iso-octyl phthalate as plasticisers.

The mixture was polymerised by heating without stirring. The resultant polymeric gel was stable at all temperatures.

The polymeric gel was blended with prepolymer at a ratio of 1:2. The viscosity of the mixture was increased so that the mixture could be used for film formation by heating during de-aeration.

To produce clear sheet with fibreglass reinforcement, the prepolymer was polymerised to appropriate viscosity by heating during de-aeration. Example 3

The procedure of Example 2 was repeated and woven fibreglass matting reinforcement was added at an effective viscosity is between 16 sees and 45 sees, the chosen viscosity depending on the percentage ratio of resin to glass required.

The ratios that can be produced by this range of viscosities is 1:2 (resin to glass) up to 2:1 (resin to glass). Resin viscosity is important in achievement of efficient wet out of the glass fibres.

For chopped strand glass mat the effective prepolymer viscosity is 20 sees to 250 sees. The lower the glass percentage, the higher the viscosity of the prepolymer has to be. Example 4

An acrylate plasticised prepolymer was prepared from prepolymer by mixing 78% acrylate prepolymer together with two plasticising agents, 3% dioctyl phthalate and 19% polymeric plasticizer.

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Example 5

500 g PVC polymer was plasticized with 300 g of plasticizer (e.g. dibutyl phthalate or dioctyl phthalate) and allowed to stand for a few minutes so that the plasticizer can be properly absorbed by the PVC. This mixture was then blended with 1200-1500 g acrylate prepolymer to form a low viscosity mixture which can be poured or knife coated onto a flat surface to form a film which can be cured with UV light at ambient temperature. The film so formed had a hardness of 55 Shore D. The hardness is determined to a large extent by the amount of plastlcizing agent added.

Industrial Applications

The ease of handling of the prepolymer compositions of the invention simplifies plant requirements for the production of products made from the solid polymers of the invention.

This leads to simplified automation of production with consequent cost benefits and a low level of expertise required for plant operators.

The polymeric compositions of the present invention are ideal for applications requiring a low level of operator expertise and/or where sophisticated plastics plant processing equipment is not available, e.g., in applications where low volume or large size makes the cost of conventional plastics moulding prohibitive, because of the size and/or cost of the dies. With the present invention, the components of the polymer mix can be mixed by hand and inexpensive timber moulds can be employed, the timber mould being coated with a suitable release agent. The polymer mix can be simply poured or pumped into the mould and allowed to cure or set.

The compositions of the present invention bond very well to most surfaces including glass and metal. The strength of the material can be enhanced by the addition of reinforcing material such as nylon or fibreglass. The polymer of. the present invention bonds much more readily to substrates and reinforcing materials than do similar polyester based systems. For example, with polyester systems a relatively high resin content in the mix is required for proper bonding, e.g., 2 parts by weight resin to 1 part by weight fibreglass. This produces rigidity and brittleness in the product, with cracks and crazing on the surface.

By comparison, the acrylic system of the present invention requires much less resin for adequate bonding, e.g., 1 part by weight resin to 2 parts by weight fibreglass, producing sheet products with much higher strength factors, and much greater flexibility.

The film forming applications of compositions of the invention provide inexpensive efficient and simple methods for production of

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waterproofing/weatherproof!ng membranes. Such membranes are suitable for uses such as building construction applications and in water conservat ⁱ on as water dam liners.

Further, the film formed by the particular combination of PVC and acrylic prepolymer is ideal for heat shrink applications, having 60% plus return.

The methods for the production of prepolymers, polymer compos ⁱ t ⁱ ons and polymer articles are of use in the preparation of articles such as flat and profiled polymer sheeting as well as other polymer articles. The processes provide an economical alternative to previous processes for the preparation of polymer compositions.

Although the invention has been described above with reference to examples and to preferred embodiments, the invention may be embodied in other forms or carried out in other ways without departing from the spir ⁱ t or essential characteristics thereof. The above description is therefore to be considered in all respects, illustrative and not restrictive, and all changes which come within the meaning and range of equivalency are intended to be embraced therein.