EP0790111A1

EP0790111A1 - Release agent for clay mouldings

Info

Publication number: EP0790111A1
Application number: EP97102117A
Authority: EP
Inventors: Reginald Van Elmbt; Lionel Van Oostende; Raymond Navette
Original assignee: Fina Research SA
Current assignee: Total Petrochemicals Research Feluy SA
Priority date: 1996-02-15
Filing date: 1997-02-11
Publication date: 1997-08-20
Anticipated expiration: 2017-02-11
Also published as: EP0790111B1

Abstract

The present invention concerns compositions for demoulding and/or forming products for the ceramic industry. As main ingredient, we can find silica or alumina. The products include refractory bricks, tiles, ceramics, roof tiles, flower pots. The use of said products is also described. The compositions are environmentally friendly.

Description

Field of the invention

Background of the invention

Since clay is found in nature, in abundant quantities, and therefore as crude product is a cheap material, it is used for the pottery production. Clays are hydrated aluminosilicates which in combination with water give a plastic paste that can easily be put in the desired shape and is highly cohesive in the humid state and after drying.
The plasticity of the paste is higher when the water content is increasing. At low water contents, practically below about 10%, the behaviour of the clay is nearly totally elasto-rigid.
Therefore, in the ceramic industry, it is preferred to work, from a technological point of view, with a water content above 10%. In this case, plasticity is higher, resistance to deformation is lower and shaping becomes easier.
For the production of clay roof tiles and other pieces such as floor tiles, pastes with moderately low water content, usually between 10% and 30% are being used. Plasticity is optimized and pottery may be shaped without too much difficulty. When metallic moulds are used, high pressure moulding or forming is necessary to obtain the desired form. Metallic moulds or stamps must be rather robust and must resist to abrasion.
The production process and the process equipment is adapted to the plasticity of the paste, influenced, as said before, by the water content of the clay. If plasticity is sufficiently high, the clay may be extruded and moulded in metallic moulds, such as in the case of the production of flower pots.
In the production of roof tiles or wall tiles, water content is generally lower than in the production of flower pots and the pressure applied in moulding or shaping is much higher.
The metallic moulds have poor release properties.Therefore the demoulding of the ceramic paste might be uneven. This occurs, in particular, when the plasticity of the paste is fairly low and when the pressures being applied are consequently higher, leading to premature wear and damage of the mould.
For this reason it is necessary to apply a release composition, either by brushing or spraying.
The requirements to be fulfilled by a composition acting as a mould release agent for clay mouldings are :

1. The composition shall substantially not affect the plasticity of the clay mixture.
2. To a certain extent, the composition shall be able to adhere to the mould.
3. The composition shall have a minimum hazardous effect on the environment.
4. The composition shall have a minimum hazardous effect on the workers.
5. The composition shall form a continuous coating on the surface of the mould, giving an excellent mould releasing effect and little abrasion of the mould and resulting in a homogenous clay surface.

Release agents containing fatty acids and/or esters have been used and are still being used for the demoulding of the ceramic articles whereas petroleum solvents ranging from the white spirit range to certain gasoils are being used as diluents. Volatility of the solvent was and is playing a role for security reasons. More heavier mineral oils such as some lubricating oil fractions are excluded for some applications.
For example, while heating in an oven, the colour of the clay, for instance the red colour of a flower pot, is due to carbon residue. For those reasons kerosene type solvents and in particular burning-kerosene type products are frequently used, as are refined solvent cuts with low aromatic content.
It is also known to use release compositions under the form of emulsions comprising less than 50% by weight on the composition of fatty ester. The common teaching is that higher ester concentrations are detrimental to the emulsion because of a too high viscosity.
Japanese Patent Application N° 97840/1975, laid-open number 20986/1977 (Nippon Sekiyu KK) describes a mould releasing agent comprising 1 part of an oily agent and 1 to 20 parts by weight of a mineral oil. The oily agent comprises 50-96% by weight of a fatty acid and 50-4% of a fatty acid ester. According to the patent application, a synergistic effect between the fatty acid ester and the fatty acid is responsible for the releasing effect. If the amount of the fatty acid ester exceeds 50% wt the mould releasing effect may be reduced.
However, the Japanese Patent Application N° 97840/1975 is relating to a mould releasing agent suitable for use in moulding products of the ceramic industry, for example moulding materials containing not more than 30% of silica or alumina as a main ingredient. The compositions described in this application are not necessarily giving excellent results on demoulding products made of clay, which is a complex mixture of hydrated aluminosilicates. For the reasons explained above, spindle oils or other lubricating oil fractions such as machine oils are not frequently being used on ceramic material predominantly made of clay.
Furthermore according to our experience in the clay ceramic industry the active oily fraction is not necessarily a synergistic blend of (i) fatty acids and (ii) fatty acid esters diluted with mineral oils. Diluted fatty acids or diluted fatty acid esters are equally giving satisfactory results.
In the Japanese Patent Application N° 91/168390, laid open number 5016129, of ASK Corporation, the release agent composition is defined as a composition obtained by diluting at least one kind of an oil and fat type release agent, a vegetable oil fatty acid ester type release agent and a surfactant with a kerosene, a super-light oil or water. The release agent and air are supplied to the mould which is prepared in gas permeable material such as sintered ceramic.
The influence of the water content of the clay on mould release properties has been noticed in the past with classical formulations in the production of flower pots. A composition containing white spirit or kerosene and fatty material such as oleic acid or an ester is giving satisfactory results on a clay containing 26% of water when the fatty acid/ester content is appropriate for example 10% wt.
In changing the production technique and in working with a clay mixture with less water, about 22%, and hence less processable, less costly in the subsequent drying and firing sequence, we have been obliged to increase the fatty acid content to 30% weight for obtaining satisfactory results in the demoulding process.
Clay less processable and dryer is requiring larger concentrations and larger amounts of fatty acids and/or esters, diluted or not in suitable organic solvents or/and in mineral oils or synthetic oils such as low viscosity base oils (spindle oils), polybutene, polyalphaolefines and the like. This requirement is partly due to the fact that higher pressures are required for processing and forming and hence the mould release agent film should be more resistant to squeezing, be of higher viscosity or/and containing considerably more fatty acids/esters.
The compositions used presently and containing a certain amount of petroleum solvent, acting as diluent or principally based on the use of said solvents are monthly giving satisfactory results as far as adherence of the clay to the mould is concerned.
These products however present several drawbacks, principally from the point of view of toxicity. The hazardous effect on the environment cannot be neglected either.
It is well known that solvents of the kerosene type present a high risk of hazardous effects on the workers particularly when the composition is sprayed but also when applied differently as the solvents evaporate at least partly during the application and immediately thereafter. The hazard is particularly important when kerosenes containing a fair amount of aromatics are being used. There is also an environmental risk as the product is not biodegradable and might penetrate the soil and spoil drinking water and as such being a hazard for the environment. When using white spirit or kerosenes with a flash point below 60°C, special precautions shall be taken to minimize the risks of explosion and fire.
In Europe, it is generally suggested to lower the use of solvents which end up in the environment as hydrocarbons influencing the formation of ozone and chemical smog.
A complete or partial ban of the use of solvents for applications classified as lost lubrication is anticipated in a near future.
For the production of coloured pottery, such as coloured roof tiles, iron oxide and manganese oxide pigments are being used. It is obvious that for price reasons these oxides are not being mixed with the clay to obtain a evenly coloured product in the mass. On the contrary the use of these pigments is being limited to the minimum. Only the upper layer is being pigmented, preferably by applying a pigment slurry to the clay surface.
The clay mould release agent and the carrier fluid used in the preparation of the slurry pigment may be different but generally problems of product compatibility and mould release are being avoided through the use of the mould release agent as carrier fluid for the pigment.
The currently used mould release compositions contain a large amount of a petroleum solvent, such as kerosene, and a small amount of a suitable fatty acid ester or a fatty acid. In a particular case the mould release composition consisted of kerosene to which 3% of lecithine of soja were added.
The mould release agent and the pigment slurry are applied to the clay surface in two consecutive steps. Alternative methods such as putting the mould release agent on the surface of the mould and the pigment slurry on the clay surface also exist.
These compositions present the same detrimental effect to the environment and to the workers as encountered with the mould release compositions used for non pigmented pottery. Furthermore the pigment has a tendency to separate and to settle down and the pigment concentration in the pigment slurry is not always constant. Some clay colouring problems are being avoided by putting more pigment slurry than theoretically required.
The present invention aims to achieve an improvement in both mould release properties and environmental properties of the clay mould release composition.
The present invention also aims, in particular, to use such mould release composition for the preparation of a pigment slurry composition used as a pigment concentrate having improved demoulding properties.
It has now been found that release agents can be formulated in a way which not only improves the biodegradability thereof but also improves its demoulding properties and at the same time exhibit a lower solvent evaporation.
The mould releasing agent of the present invention is a novel composition correcting defects of the conventional products. The mould releasing agent of the present invention is effective for the moulding of clay products and particularly effective when using a metal mould.
The present invention provides for a mould release composition for the clay ceramic industry which comprises

a wetting agent
an ashless dispersant
a polar solvent
an oily agent
optionally another solvent

a) a fatty acid or a mixture of fatty acids, saturated or unsaturated, linear or branched from C₆ to C₂₂, or
b) a fatty acid ester or a mixture of fatty acid esters of C₆ to C₂₂ fatty acids, saturated or unsaturated, linear or branched, and of a monofunctional alcohol from C₁ to C₂₂, linear or branched, saturated or unsaturated or of a polyfunctional alcohol with a maximum of six (6) OH groups,

According to the present invention, it is appropriate to use fatty esters and/or fatty acids which are liquid at the operating conditions. Particularly suitable fatty acids are those resulting from unsaturated fatty acids having from 16 to 22 carbon atoms and alcohols having from 1 to 6 carbon atoms, or those esters resulting from saturated fatty acids having from 6 to 10 carbon atoms with alcohols having 1 to 12 carbon atoms.
Generally the oily agent represents more than 50% by weight of the composition and particularly more than 75% by weight. In certain circumstances, the oily agent may be used in amounts higher than 85% by weight on the total composition.
As example of a wetting and/or antiwear agent we can cite :

a) a composition containing an alkali or an alkaline earth metal.
The presence of such a metal composition in the mould release agent provides the release agent with the ability to spread the product more evenly and uniformly on the surface of the mould and the surface of the clay whereby a uniform film is not disturbing the drying process in an oven avoiding deformation of roof tiles on drying or baking.
The metal containing composition may be an alkali metal or an alkaline earth metal salt or sulfur acids, carboxylic acids, and phenols.
The basic and neutral salts can be of ester-soluble organic sulfur acids such as sulfonic, sulfamic, thiosulfonic, sulfinic, sulfenic, partial ester sulfuric, sulfurous and thiosulfuric acid. Generally they are salts of sulfonic acids.
A specific example of a derivative of an oil soluble sulfonate, particularly useful in the invention, is a sodium sulfonate with a molecular weight of about 410.
b) an alkali or earth alkali metal containing carboxylic acid such as an aliphatic substituted salicylic acid.
c) an alkali or earth alkali metal salt derived from alkenyl succinic acid or alkenyl sulfusuccinic acid.
d) salts of phenols generally known as phenates.

The mould release composition may also comprise a hydrocarbon-soluble ashless dispersant. The compounds useful as ashless dispersants generally are characterized by a polar group attached to a relatively high molecular weight hydrocarbon chain. In general, any of the ashless detergents which are known in the art for use in lubricants can be utilized in the present invention.
In one embodiment of the present invention the dispersant is selected from the group consisting of

hydrocarbyl substituted amine including monamines such as PIB or polyamines such as PIB tetraethylene pentamine
acylated nitrogen containing compounds
nitrogen containing condensation of phenols, aldehydes and aminocompounds
esters of substituted carboxylic acids
lecithine of soja

The composition of the invention may also comprise any polar solvent with high superfacial tension above 30 Nm^-1 such as water.
The mould release agent may optionally contain, depending on the original blend, a solvent, preferably a polar solvent and more preferably a biodegradable polar solvent acting partially as a viscosity regulator; typical examples of polar solvents which may be used include :

lower alcohols such as monovalent alcohols from C₁ to C₁₃, ethanol being an example,
polyvalent alcohols with a maximum of 6 OH groups, such as glycerol and trimethylol propane,
natural occuring products such as turpentines,
substantially biodegradable low molecular weight hydrogenated oligomers of 1-alkene hydrocarbons,
oxygenated solvents, preferably ethers.

Other solvents such as petroleum solvents may be used but they are not preferred for biodegradability reasons.
The mould release agent may furthermore contain for storage stability reasons some antioxidant. The type and amount of suitable antioxidant is sufficiently described in literature and is well known.
It is understood that the amount of wetting agents, ashless dispersants, polar and/or non polar solvents represents a maximum of 50% by weight of the composition.
In addition, the Applicants have unexpectedly found that when pigments are used with the mould release composition, the amount of pigments to be used is drastically reduced with regard to usual amounts; such reduction may reach 15% by weight or even more.
The invention is described more in detail with reference to the following examples.

Example 1

The clay paste used for the production of roof tiles has a water content of 23%. The clay, after being processed and homogenized in a kneader, is passed through an extruder and further conveyed on a transport belt in the form of a continuous rectangular block.
The pigment slurry is a mixture of manganese oxide and a mould release agent. The pigment slurry which is prepared and stored in a product tank has the following composition :

manganese oxyde: : 50 kg
mould release agent: : 17 l

The density of the slurry is about 2,147 kg/l and the viscosity cup Ford n°4 is 49 seconds at 20°C.
The mould release agent has the following composition by weight.

Oily agent : rape seed oil methyl ester (RME) : 95%
wetting agent : sodium alkylbenzenesulphonate (molecular weight 405, Synacto® 405 of Esso Chemical): 4%
polar solvent having superfacial tension > 30 Nm^-1 : water : 1%

The viscosity of the mould release agent is 4,2 mm²/s at 40°C and its density is 0.880.
The pigment slurry, pumped with a peristaltic pump, drops on the rectangular clay block leaving the extruder. The amount of pigment slurry applied is 2g per roof tile, which in this example is 58 ml/minute. Immediately thereafter the pigment slurry is uniformly spread on the clay surface by means of two brushes and the clay surface is subsequently cut up by a knife to the desired length. The rectangular clay blocks, having approximately the dimensions of the roof tile, first pass through a machine to be pressurized. This improves the compactness of the clay without changing the form of the clay block. The clay blocks are finally put in a machine with three revolving moulds, each with a piston pushing the clay in the desired form by a kind of forming process. The tiles are demoulded and dried at a temperature of about 40°C alongside the walls of the furnace. The are finally fired in a furnace at 950°C.
Clay roof tiles with a uniformly black colour are being produced with no tile rejection based on colour defects, other surface defects or cracks.

Example 2 (comparative)

The mould release agent is a mixture of kerosene and 3% of lecithine of soja.
The above-described mould release agent is stored in a product tank and the pigment slurry, containing a blend corresponding to a mixture of 50 kg of manganese oxide and 24 l of mould release agent, is stored in a second product tank. The density of release agent is 0,840 kg/l.
The density of the slurry is 1,532 kg/l and the viscosity of the slurry is cup Ford 4 : 30 seconds at 20°C. Both mould release agent and pigment slurry are pumped through separate peristaltic pumps through separate product lines. Preoiling takes place with the pure release agent at a rate of 40 ml/min and the pigment slurry is dropping on the clay surface at a rate of 60 ml/min, corresponding to 5,2 g/tile immediately thereafter.
In this particular process the release agent and the pigment/release agent slurry are dropping onto the clay.
The clay roof tiles have a quite uniform black colour with no tile rejection based on a lack of colour uniformity.
In comparaison with example 1 the mould release composition of the present invention unables to decrease the consumption of the pigment by about 15% by weight based on the total consumption of pigment and we note also a reduction of the amount of mould release agent of about 50% by weight.

Example 3 (comparative)

The mould release agent and the pigment slurry are identical to those of example 2, but the quantity of the pigment slurry is lowered to match the same amount of pigment per tile as in example 1.
Production is impossible, not due to demoulding problems, but because of differences in colour on the clay tile, giving therefore a 100% rejection.
It is therefore proven that the quantity of pigment applied in the prior art must be higher than the pigment/mould release agent slurry of the present invention.

Example 4

The following mould release agent is prepared with (% by weight)

Oily agent : rape seed oil methyl ester (RME) : 90%
Wetting agent : sodium alkylbenzenosulphonate (molecular weight 405, Synacto® 405 of Esso Chemical): 6%
Polar solvent : water : 4%
viscosity of the mould release agent : 4,6 mm² at 40°C
density of the mould release agent : 0,895

Thereafter, a pigment slurry is prepared by blending :

50 kg of manganese oxide and
18 l of release agent

viscosity of the pigment slurry cup Ford n°4 : 46 sec at 20°C
density of the pigment slurry : 2,020
water content of the clay : 23%

The pigment slurry is applied as in example 1. The clay roof tiles have a uniform black colour with no product rejection.

Example 5

The following mould release agent is prepared with (% by weight)

Oily agent : 2-ethylhexyl oleate : 92%
Wetting agent : sodium alkylbenzenosulphonate (molecular weight 405, Synacto® 405 of Esso Chemical) : 5%
Polar solvent : water : 3%
viscosity of the mould release agent : 4,4 mm²/s at 40°C
density of the mould release agent : 0,875

Thereafter, a pigment slurry is prepared by blending :

50 kg of manganese oxide and
18 l of release agent

viscosity of the pigment slurry cup Ford n°4 : 44 sec at 20°C
density of the pigment slurry : 1,995
water content of the clay : 23%

Claims

Mould release composition for the clay ceramic industry which comprises
- a wetting agent

- an ashless dispersant

- a polar solvant

- an oily agent

- optionally another solvant
characterized in that the oily agent represents at least 50% by weight of the mould release composition and is constituted of
a) a fatty acid or a mixture of fatty acids, saturated or unsaturated, linear or branched from C₆ to C₂₂, or

b) a fatty acid ester or a mixture of fatty acid esters of C₆ to C₂₂ fatty acids, saturated or unsaturated, linear or branched, and of a monofunctional alcohol from C₁ to C₂₂, linear or branched, saturated or unsaturated or of a polyfunctional alcohol with a maximum of six (6) OH groups,
Mould release composition according to claim 1 wherein the oily agent represents more than 75% by weight of the composition.
Mould release composition according to claims 1 and 2 wherein the oily agent represents more than 85% by weight of the composition.
Mould release composition according to claims 1 to 3 wherein the oily agent is constituted of fatty esters and/or fatty acids which are liquid in the operating conditions.
Mould release composition according to claim 4 wherein the fatty esters are resulting from unsaturated fatty acids having from 16 to 22 carbon atoms and alcohols having from 1 to 6 carbon atoms.
Mould release composition according to claim 4 wherein the fatty esters are resulting from saturated fatty acids having from 6 to 10 carbon atoms and alcohols having from 1 to 12 carbon atoms.
Mould release composition according to claims 1 to 6 wherein the oily agent is selected from rapeseed oil methyl ester and 2-ethylhexyl oleate used in an amount of minimum 90% by weight of the composition.