GB2049699A - Process for Obtaining Reinforced Cellular Materials Based on Unsaturated Polyester Resins - Google Patents

Abstract

Cellular materials are obtained from unsaturated polyester resins reinforced with fillers having a density below 0.7 kg/lt by injecting a liquid foam, made from the resins by mechanical introduction of a gas therein into a closed mould. The liquid foam, including additives and optionally a reinforcement of synthetic, artificial, vegetable or mineral fibres having a length lower than 5 mm, and optionally containing a low boiling foaming agent, is injected and cross-linked in the hot or in the cold in a closed mould containing a reinforcing agent of synthetic, artificial, vegetable or mineral fibers as a monofilament mat, a cut fibre mat, a mono- or bi- directional roving woven mat, rovings, or fabrics.

Description

SPECIFICATION Process for Obtaining Reinforced Cellular Materials Based on Unsaturated Polyester Resins The present invention refers to a process for making reinforced cellular materials from unsaturated polyester resins by injecting a liquid foam, made from said resins by mechanical introduction of a gas therein, into a closed mould containing the reinforcing materials which will be hereinafter specified.

The present invention also refers to the cellular materials thus obtained, as well as to the products made from said cellular materials.

Moulded cellular materials of reinforced unsaturated polyester resins are known. Said materials however are obtained by impregnating the reinforcing material with an unsaturated polyester resin in liquid form, which resin is successively chemically expanded in the mould. Said process however has the following disadvantages: the chemicals employed as foaming agents are usually toxic and further are generally unstable at room temperature and therefore must be maintained at low temperatures until their use; the process is not economical since the chemical foaming agent is expensive; the process requires moulds suitably reinforced to stand the pressure produced during the expansion of the liquid resin.

A method for overcoming these disadvantages has been proposed in the art. It consists in carrying out the foaming by mechanical incorporation of the gas into the liquid resin. This method however does not permit to incorporate a reinforcing material having a length greater than 1.5 mm before the foaming stage, inasmuch as the mechanical devices for gas dispersion (nozzles and turbines) do not permit the passage of larger reinforcing materials and further such materials also cause a partial degradation of the foam.

A method for overcoming this last difficulty has also been proposed, which consists in separately preparing the foam by mechanical means and injecting it in liquid form into a closed mould in which a bed of dry fibres has been previously placed, which fibres are constituted by a mat of glass fibres cut and disposed over the entire cross-section of the mould or fixed on the two halves of the mould.

However, not even this method is free from disadventages: the styrene contained in the liquid resin dissolves the binder which keeps the mat together and the entering flow of foam removes the glass fibres: in the case of a mould containing the reinforcement in the form of a mat of glass fibres which are cut and disposed over all the cross-section of the mould, said reinforcement does not permit the foam to pass through without breaking it.

The applicant has now surprisingly found a method for producing cellular materials from unsaturated polyester resins, reinforced with reinforcing fillers and having a density lower than 0.7 kg/lt, whereby said disadvantages are overcome.

An object of the present invention is therefore a process for obtaining cellular materials from unsaturated polyester resins, reinforced with reinforcing loads, having a density lower than 0.7 kg/lt, by injection into a closed mould, of a liquid foam of said resins, obtained by mechanical introduction of a gas, characterized by the fact that the liquid, foam made of unsaturated polyester resins which contain conventional additives, optionally containing a reinforcement of mineral or organic fibres having a length lower than 5 mm, preferably less than 3 mm and more preferably less than 1.5 mm, obtained by mechanical introduction of a gas, and optionally containing a low boiling foaming agent, is injected and subsequently cross-linked in a closed mould containing a reinforcing agent of synthetic, artificial, vegetable or mineral fibres in the form of a monofilament mat, a cut fibre mat, a mono- or bidirectional roving mat, rovings, fabrics or the like.

In the case that a cut fibre mat is used, it is convenient to use a product containing a binder which has a low solubility in styrene, so as to avoid its being washed away and the consequent displacement of the fibres.

Preferably glass fibres are used as reinforcing material.

The reinforced cellular material made of unsaturated polyester resins thus obtained, is also an object of the present invention, said cellular material preferably has a percentage of closed cells above 80%.

If the monofilament mat is employed as reinforcing agent in the mould, a cellular material is obtained which is uniformly reinforced along all its thickness, viz. the fibres are uniformly and homogeneously distributed through the entire body of the product.

In the case that a woven mat, rovings or fabrics are used as reinforcing fillers in the mould, a cellular material is obtained which is uniformly reinforced over all its surface in a stable way.

The cross-linking in the mould may be carried out, according to the present invention, both in the hot and in the cold, preferably between 20O and 800C.

The percentage of reinforcing material is preferably between 5 and 50% by weight with respect to the unsaturated polyester resin.

If glass fibres are used as reinforcing agent in the mould, said fibres have a diameter which is smaller than 1 6 micron. If other synthetic, artificial, vegetable or mineral fibres, such as e.g. aramide, carbon, cellulose ester, polyethyleneterephthalate, acrylic, or regenerated cellulose fibres are used as reinforcing material, said fibres have a count lower than 20 deniers.

The liquid unsaturated polyester resin foam, optionally containing the low boiling liquid agent and/or the reinforcing fibres having the aforesaid lengths, is conveniently obtained in a foaming machine constituted by a turbine having numerous ranks of vanes having a peripheral speed of 200500 mt/min, said turbine being heated by means of suitable jackets and each row being separated from the following one by crowns of pegs fixed on the jacket of the turbine itself. In the case that a low boiling liquid agent and/or fibres of the reinforcing material hereinbefore specified are used, a stirrermixer is conveniently inserted before said turbine, in which stirrer-mixer the solution of unsaturated polyester resin and styrene, containing suitable additives, is mixed with the low boiling liquid agent and/or the fibres of reinforcing material.

A fluid (preferably nitrogen or air) which constitutes the foaming agent is also introduced into said turbine at an appropriate pressure. The catalyst is introduced in the last row of the turbine, wherein the foam has already been created, in such a way that the foam which flows out of the turbine already contains the catalyst.

The injection of the liquid foam is conveniently effected by using a pressurized vessel exploiting the inner pressure of the vessel and controlling the minimum and maximum leveis according to conventional methods.

The closed moulds (constituted by at least two halves), into which the liquid foam is injected, may be of metal or of a composite material, and in any case do not require any particular strength, contrary to what occurs when foams are made by chemical expansion of the resin where the high pressures which are reached require especially high resistance and rigidity of the moulds.

It is therefore apparent that the present invention is economically convenient, since stronger moulds are much costlier.

If catalytic systems which operate in the hot are used, the moulds may be heated, whereby advantages are obtained as to polymerization times and surface finish of the products. Before the injection, if synthetic or artificial, vegetable or mineral fibres having a length higher than 1,5 mm, such as monofilament mat, cut fibre mat, woven mat, roving, mono- and bidirectional fabrics, etc. are used, said reinforcement fibres, in the dry state, are preferably previously positioned in the moulds.

The appropriately catalyzed liquid foam introduced into the mould, wets the fibres positioned therein at the moment of its injection without changing their disposition in the mould, and subsequently polymerizes.

The polymerization reaction may be primed either in the cold or in the hot, depending on the catalytic system employed and on the purposes which are to be attained. The expression "unsaturated polyester resins" is to be construed, according to the present invention, as meaning the resins obtained from an unsaturated polyester, formed by polycondensation of at least one a-w ethylenically unsaturated dicarboxylic acid and/or at least one corresponding anhydride with at least one polyvalent alcohol, and one or more ethylenically unsaturated monomers, such as e.g. styrene, vinyltoluene, methylstyrene, methylmethacrylate, diallylphthalate, etc.

Examples of ethylenically unsaturated dicarboxylic acids or corresponding anhydrides comprise maleic acid or its anhydride, fumaric, itaconic and mesaconic acids.

Together with the unsaturated dicarboxylic acids there may be employed mono or polyfunctional aliphatic, saturated carboxylic acids such as adipic, succinic, glutaric acid and the like; mono or polyfunctional aromatic carboxylic acids such as phthalic, isophthalic, terephthalic, benzoic acids etc.; anhydrides such as phthalic, trimellitic anhydride etc.

As polyvalent alcohols there may be employed: ethylene glycol, propylene glycol, 1 2-butanediol, diethylene glycol, dipropylene glycol, 1,6-hexanediol, 1 ,4-cyclohexanedimethanol, trimethylolpropane, pentaerythrite, glycerine, neopentylglycol, etc.

The unsaturated polyester resins may be prepared by the known processes used for the plyester resins, both in solvent and in dry phase.

According to a practical preferred embodiment of the present invention, the unsaturated polyester resin is obtained by reacting from 1 to 1.3 mols of at least one polyvalent alcohol with 0.05 to 1 mol of at least one ethylenically unsaturated dicarboxylic acid and anhydride. The polycondensation is continued until a polymer is obtained having an acid number comprised between 5 and 90 mg of KOH/g. the preferred acid number is comprised between 10 and 30 mg of KOH/g and the molecular weight between 500 and 5000.

Besides the ethylenically unsaturated dicarboxylic acid or correspondent anhydrides, a saturated dicarboxylic acid may be present in the mixture, in a molar amount comprised between 5 and 95% with respect to the unsaturated dicarboxylic acid, according to the known art.

The unsaturated polyester thus obtained is mixed with styrene, in a polyester/styrene ratio comprised between 9:1 and 1:1 preferably between 4:1 and 2.5:1.

Inhibitors and stabilizers adapted to prevent the premature cross-linking of the mixture may be added to the styrene/unsaturated polyester mixture, in amounts from 0.1 ppm to 10000 ppm.

The most commonly used inhibitors and stabilizers are: hydroquinone, quinone, quinidrone, tertiary butylpyrocatechol, toluene hydroquinone, monotertiary butylhydroquinone, ditertiary butylhydroquinone, 1 ,4-naphthoquinone, anthraquinone, methyl and/or ethyl ethers of hydroquinone, picric acid, trinitrobenzene, paraphenylenediamine, etc.

Further, in order to improve the stability of the resin, organic or inorganic compounds soluble in the polyester, quaternary ammonium salts, etc., are added.

In order to improve the stability of the foam, additives are added to the unsaturated polyester resin before foaming, such as e.g. surface active agents for improving the formation of the foam and/or agents for regulating the diameter of the gas bubbles and/or agents for stabilizing the foams, e.g.

surface active agents based on silicone compounds, block copolymers of silicones with polyethers, soaps such as ricinooleates, polymercaptanes, etc.

Any compound or mixture of compounds which generate free radicals under the particular conditions of the polymerization may be used as catalytic system.

These compounds are: the peroxides or the hydroperoxides, such as diacetyl peroxide, benzoyl peroxide, hydrogen peroxide, cumene hydroperoxide, methylethylketone peroxide, etc. Other catalysts which generate free radicals may also be used such as e.g. ammonium persulphate, perborates and percarbonates.

It is preferred to employ, in addition to the free radical generating catalyst, an accelerator which increases the speed of decomposition of the peroxidic compounds, which thus produces free radicals at higher speeds. Cobalt naphthenate is generally used as accelerator and is diluted in styrene until it is brought to a concentration of about 13% of metal.

A complexing agent for increasing the efficiency of the accelerator may also be used. According to a widely accepted interpretation, it is believed that such agents act to reduce the cobalt naphthenate which is transformed in to the corresponding cobaltous compound which is much more reactive.

Generally tertiary aromatic amines, among which preferably dimethylaniline, are used as complexing agents.

Wide variations and changes may be effected in the details of the embodiment of the present invention without departing from the spirit and the scope of the present invention.

In order better to illustrate the inventive concept of the present invention and the way of carrying it into practice, some non limitative examples are described.

Example 1 100 kg of polyester resin are introduced in a steel vessel, which resin has been prepared by reacting the following components according to the following molar ratios: propylene glycol 0.8 mols, diethylene glycol 0.2 mols, maleic anhydride 0.6 mols, phthalic anhydride 0.4 mols, hydroquinone 100 ppm, styrene 30% of the total.

500 ml of cobalt octoate having a concentration of 6% in xylene, 1 kg of silicone oil, 5 kg of glass milled fibres having a nominal length of 1 mm are added to the aforesaid resin. The whole is mixed with an helical stirrer for 20 minutes. Said mixture is transferred from the vessel to a turbine thermostatized at 350C, with the help of a gear pump having a flow rate of 200 It/h. The aforesaid turbine is constituted by a stator and a rotor provided with projections having a circular cross-section.

The peripheral speed of the rotor is 250 mt/min. The foaming gas (air) is injected into the turbine through a nozzle. The catalyst, methylethylketone peroxide, is injected at a flow rate 1.6 It/h before the exit of the foam from the said turbine.

The liquid foam thus formed is poured into a vessel adapted to be pressurized. Once it has been filled, the vessel is pressurized and the liquid foam is injected through a suitable pipeline into a steel mould heated at the temperature of 600C. A monofilament mat with a weight of 600 g/m2 has been previously positioned in the mould. The cross-linking is allowed to occur, and it occurs without development of heat.

Once polymerized, the cellular material thus obtained in extracted from the mould. It has the following characteristics: Density 0.43 kg/lt Resistance to tension 128 kg/cm2 Tension modulus 14000 kg/cm2 Elongation at break 1.44% Resistance to shear 56 kg/cm2 Shear modulus 1070 kg/cm2 Minimum height from which a steel ball of 5 kg must fail to break a sample 300 cm Thermal conductivity 0.031 Kcal/m h OC Example 2 The operations are carried out as in Example 1 except that the hardening system is modified inasmuch as methylethylketone peroxide is still used but in a percentage of 1.2% of the resin which is further accelerated with dimethylaniline in an amount of 0.1% of the resin. Further, in this case the mould is not preheated and the injection occurs at room temperature.

The characteristics of the cellular material obtained are substantially the same as those of Example 1.

Claims (12)

Claims

1. Process for obtaining cellular materials from unsaturated polyester resins, reinforced with fillers having a density below 0.7 kg/lt by injecting into a closed mould, a liquid foam of said resins, made by mechanical introduction of a gas, characterized by the fact that a liquid foam made from unsaturated polyester resins including conventional additives, optionally containing a reinforcement of synthetic, artificial, vegetable or mineral fibres having a length lower than 5 mm, preferably lower than 3 mm and more preferably lower than 1.5 mm, obtained by mechanical introduction of a gas, and optionally containing a low boiling foaming agent, is injected and subsequently cross-linked in a closed mould containing a reinforcing agent of synthetic, artificial, vegetable or mineral fibres in the form of a monofilament mat, a cut fibre mat, a mono or bi-directional roving woven mat, rovings, fabrics.

2. Process according to Claim 1, characterized by the fact that the cross-linking in the mould may be carried out both in the hot and in the cold.

3. Process according to Claim 1 or 2, characterized by the fact that the percentage of reinforcing material is maintained between 5 and 50% by weight with respect to the unsaturated polyester resin.

4. Process according to at least one of the preceding claims, characterized by the fact that glass fibres having a diameter less than 1 6 micron are employed as reinforcing agent positioned in the mould.

5. Process according to one of the preceding claims, characterized by the fact that the liquid foam of unsaturated polyester resins, optionally containing the low boiling liquid agent and/or the reinforcing material fibres, is obtained in a foaming machine constituted by a turbine having many rows of vanes having a peripheral speed of 200-500 mt/min, said turbine being heated by means of suitable jackets and each row being separated from the following one by a crown of pegs fixed on the jacket of the turbine itself.

6. Process according to Claim 5, characterized by the fact that the injection of the preformed liquid foam is conveniently carried out by means of a pressurized vessel exploiting the inner pressure of the vessel and controlling the minimum and maximum level according to conventional methods.

7. Process according to one of the preceding claims, characterized by the fact that the crosslinking in the closed mould is effected at a temperature comprised between 200 and 800C.

8. Cellular reinforced material of unsaturated polyester resins, characterized by the fact that it is obtained by the process according to the preceding claims.

9. Reinforced cellular material of unsaturated polyester resins according to Claim 8, characterized by the fact that it has a percentage of closed cells above 80%.

10. Process as claimed in Claim 1 and substantially as hereindescribed.

11. Process for obtaining cellular materials from unsaturated polyester resins, substantially as herein described with reference to Example 1 or 2.

12. The features as herein disclosed, or their equivalents, in any novel selection.

New Claims or Amendments to Claims filed on 15 Aug 1980.

Superseded Claims 1.

New or Amended Claims: Claim 1, in last two lines delete "rovinq woven mat" and insert "woven rovina".