US 2721504 A
Description (OCR text may contain errors)
United States Patent PROCESS FOR IMPREGNATIN G FIBRE MATERIALS Bengt Johan Yngve Mossberg and Ernst Holger Berti] Nystriim, Djurshoim, Sweden, assignors to Aktiebolaget Statens Skogsindustrier, Stockholm, Sweden, a company of Sweden No Drawing. Application July 2, 1951, Serial No. 234,918
Claims priority, application Sweden July 14, 1950 12 Claims. (Cl; 9239) The present invention concerns the impregnation of fibre materials, such as cardboard, wallboard, chipboard and the like, in which the impregnating agent may consist of synthetic resins both of a thermoplastic character, such as polyvinylchloride, and of a thermosetting character, such as aminoplast, phenoplast, alkydresin, and further, of raw or treated linseed oil, soya bean oil, tall oil or the like, or compounds or combinations of the above or similar substances.
Hitherto, in the imgregnation of fibre materials the impregnating agent has been chiefly applied either in quantities of 0.1-1.0% or in quantities of 642%, based on the dry weight of the fibre material. Quantities within the intermediate range (1-6%) have also been used, although more seldom for reasons set out hereafter. Impregnation with the smaller quantities within the range of 0.l1.0%, such as the addition of so-called sizing medium in board manufacture, has generally been carried out by adding the impregnating agent in the form of an aqueous emulsion while the fibre material is in aqueous suspension. An addition of the impregnating agent at this stage of the manufacturingprocess and in this manner is, however, accompanied by losses of considerable amounts of the impregnating agent which are carried away with the water removed in the board forming process, and this has hitherto prevented the use of large quantities of the impregnating agent in accordance with this method. In cases where it was desired to apply large quantities of the impregnating agent, therefore, it was customary to proceed in such a way that the fibre material after receiving its final form was immersed in the impregnating agent, or in a solution of the same in a cheap solvent such as kerosene.
The method of performing impregnation by a special immersion process has many disadvantages. It is expensive to carry out, since it requires extensive apparatus and mechanical equipment. Furthermore, it is difiicult to fix the content of the impregnating agent uniformly in the fibres within the desired narrow limits owing to the fact that different parts of the same fibre material frequently absorb the impregnating agent at different rates. When the impregnating agent is employed in the form of a solution it is easier to obtain the desired degree of impregnation, but in such a case the solvent must either be removed by evaporation or recovered. Evaporation of the solvent involves great drawbacks from many points of view, amongst others, the risk of fire, since the solvents'here in question are highly inflammable. If expensive solvents are employed which must be recovered, this entails the use of extensive apparatus. In many cases the desired impregnating agent may have such a high viscosity, however, that it cannot be used in an undiluted form. Generally, with regard to the requirement to obtain a uniform impregnation and a moderate consumption of solvent, an immersion process is technically applicable only in cases when using the said relatively high contents of the impregnating agent.
2,721,504 Patented Oct. 25, 1955 The present invention provides a satisfactory solution, both from a technical and economic point of view, of the problem of impregnating fibre materials both with amounts of impregnating agent lying within the two above-mentioned ranges, 0.011.0% and 6-12%, respectively, and also in the intermediate range, 1.06%.
According to the invention the impregnation is carried out of a stage in the manufacturing process at which the fibre material already forms a continuous fibre felt but before it has attained its final form by pressing at high pressure against a polished plate or between a polished plate and a wire net or screen, the impregnating agent being applied to the side of the fibre felt turned towards the polished plate so that by hot pressing against the plate it is subsequently caused to penetrate into and either become homogeneously distributed in the fibre felt throughout its entire thickness or only to penetrate into the same to a limited depth, at the same time forcing out any water in the felt through the side of the latter turned away from the polished plate partly in the form of steam. After accomplished pressing the fibre board thus treated is subjected to a heating in the presence of air at a sufficiently high temperature for a sufiicient time for etfecting a hardening of the impregnating agent and the fibre material.
The process according to the invention has many advantages.
It is possible to exactly regulate and control the quantity of the impregnating agent used for the impregnaq tion by regulating the dosage thereof. impregnating agents which are highly viscous can also be employed with advantage, since during the following hot pressing operation they are caused to flow to the desired extent, even without the presence of a solvent. The amount of the impregnating agent applied which is actually utilized for the impregnation is very high, and even higher under certain conditions, which appreciably reduces the costs of the impregnation in comparison with the processes formerly employed.
In view of the fact that the impregnating agent is caused to flow through the fibre material during the pressing operation, the fibre material will be impregnated very uniformly. Generally, the treatment is carried out in sucha way that the impregnating agent completely penetrates the entire mass of the fibre felt, whereby an impregnated material is obtained which has excellent properties as well regarding the strength of the fibre material as its resistance to water. For certain purposes, however, it may be preferred to limit the depth of the impregnation, and in such cases the impregnating agent is so selected with regard to its viscosity and added in such a quantity that under the pressure and temperature conditions adopted in pressing, it will only penetrate and impregnate that part of the fibre felt which is adjacent to the polished plate. In this case also an excellent result is obtained. Moreover, when working in this manner, a special advantage is secured, inasmuch as on selecting an impregnating agent which hardens with sufficient rapidity, the impregnating agent will be concentrated merely in the surface layer of the board which entails a reduction in the consumption of any coating materials which may be applied subsequently to the board.
Especially suitable impregnating agents according to the invention are products of unsaturated higher fatty acidsor oils containing such fatty acids or rosin acids, such as linseed oil, soya bean oil, tall oil and the like modified with a dienophil compound, such as maleic acid or maleic acid anhydride or fumaric acid, and esterified with one or more polyhydric alcohols, such as glycerol, glycol, sorbitol and pentaerythrite. A specific example of an impregnating agent of this kind is the product obv tained from tall oil by modifying it with maleic acidanhydride and then esterifying with glycerol. The composition of tall oil modified with maleic acid anhydride is not definitely ascertained but may be supposed to be according to the following formula:
When treating this product with glycerol all acid groups therein are esterified.
As other examples of impregnating agents which may advantageously be used according to the invention may be mentioned for example linseed stand oil, phenol formaldehyde resins and urea formaldehyde resins, the two latter suitably in state of oil-modified products, and alkyd resins.
According to circumstances, the impregnating agent may either be applied as such, or in the form of an emulsion, or in the form of a solution, and it may suitably be applied to the fibre felt by coating or spraying. According to a preferred embodiment of the invention the impregnating agent is added in the form of an aqueous emulsion with water as the continuous phase.
If desired, two or more different impregnating agents may be used which can either be added in a mixture or one after the other in different steps.
When carrying out the invention, the treatment is adopted to the existing conditions regarding the kind of the fibre material, the thickness and structure of the fibre felt, the kind and viscosity of the impregnating agent, the desired content of the impregnating agent to be fixed in the fibres, the temperature in the pressing operation etc., which have a mutual relation to one another. Generally, in case of a given fibre material, the treatment has to be carried out under conditions which regarding temperature, time and pressure lie within very narrow limits. The most suitable working conditions may be easily ascertained by preliminary tests.
When applying the invention in practice it has been found suitable to employ an impregnating agent having a viscosity of from about 2000 to 5000 cps. at C., in case of a complete impregnation of the fibre felt throughout its thickness. In case of a partial impregnation of the felt, the impregnating agent may have a viscosity of from 300 to 2000 cps. at 20 C., or even lower than 300 cps. The pressing of the felt after application of the impregnating agent thereto is preferably carried out in one or more periods of at least to seconds at a full pressure of 15 to kg./cm. at a temperature within the range of about to 220 C., the total period of pressing varying from about 6 to 20 minutes depending on the temperature and pressure conditions used and the properties of the fibre material. The final hardening of the impregnated board material is then preferably effected by heating to a temperature of about to 200 C., for 9 to 12 hours at the lower temperatures within said range, down to about 1 hour at the higher temperatures in the neighbourhood of 200 C.
If the impregnating medium is added in the form of an aqueous emulsion it is necessary to employ an emulsifier which gives an acid pH-reaction during the subsequent pressing operation. Suitable examples of such emulsifiers are ammonium compounds of fatty acids which at the temperature prevailing during pressing are decomposed so that free ammoniac is given. off in a gaseous form.
Alkali compounds cannot be employed as emulsifiers withoutcertain measures, as the alkaline reactionof the water in such a case would cause adhesion of the fibre material to the polished plate used in pressing. However, it is also possible to use alkali compounds as emulsifiers, on the condition that in that part of the felt which during pressing is in contact with the polished plate, the
necessary acid pH-reaction is produced in some other manner, for example by subsequent spraying sulphuric acid on the fibre felt before it reaches the polished plate, which however, is an inconvenient solution from a technical point of view.
Substances with an additional etfectmay also be added to the impregnating agent. Thus, in certain cases, it may be desirable to incorporate additives such as insecticides or fungicides in the board material and for this purpose such substances may be added to the impregnating agent. As suitable examples hereof may be mentioned tetra and pentachlor phenol, chlornaphthalins etc. or their salts. Further, also colouring agents may be added.
Thus, it is highly desirable for certain purposes to give a certain shade of colour to wallboard, such as brown for example. This can be combined with an addition of substances which accelerate the hardening for some of the synthetic resins used as impregnating agents, such as siccatives which in the absence of other colouring pigments can impart a certain colour to the surface of the board. For example, with an iron siccative, such as iron naphtenate, linoleate or rosinate, an approximately grey colour is obtained, whilst the corresponding manganese compounds give the board a colour tending towards brown. The quantities required for producing these effects correspond to the quantities employed for obtaining the siccative efiect, that is to say, they are of the order of magnitude of 0.1-1.0% metal, based on the quantity of the impregnating medium.
The application in practice of the process according to the invention is more particularly described below in the following non-limitative examples.
Example 1 In the impregnation of wallboard for the production of, so-called oil-tempered board, the oil used as impregnating agent is applied to the upper side of the fibre felt which during subsequent pressing in a high pressure press is turned towards the polished plate, at a point immediately following the last pair of rolls of the board machine, or fourdrinier'forming machine, from which the fibre felt to be impregnated is delivered. As impregnating agent, a tall oil product modified with maleic acid anhydride and esterified with glycerine (see above) and having a viscosity of 2000 to 5000 cps. at 20 C. may be employed. For entirely homogeneous impregnation of the felta quantity of this oil is added corresponding to 6 to 8% of the dry weight of the fibre.
The oil is added in the form of an emulsion of oil-inwater with a concentration of 1 part oil to 7 parts water. When preparing the emulsion ammonia is added, this addition together with the free fatty acid groups of the talloil product serving as an emulsifier. The emulsion is applied from two rows of spraying pipes provided with nozzles, whereby a perfectly uniform surface coating is produced on the felt. When the oil emulsion encounters the upper side of the fibre felt it is broken down.
After impregnation, the fibre felt is transported into a high-pressure press where pressing takes place at a pressure of 50 kg./cm. at a temperature of 200 C. During this pressing operation the fibre felt is first subjected to the full pressure of the press for a period from two, up to several tens of seconds, whereupon the pressure is reduced down to for example 8 to 10 atmospheres and the residual water in the fibre mass is allowed to boil off, whereafter the felt thus treated is again subjected to the full pressure for a number of minutes. The total pressing-cycle can hereby be varied within certain narrow limits depending upon the quality of board required. With the oil impregnation described above, in order to enable the oil to penetrate the felt homogeneously, it is preferred to employ a first high-pressure period of 30 to 45 seconds. Under the pressure and temperature conditions stated above, the viscosity of the tall oil product Will decrease in such a way that the oil isdistributed n ale homogeneously throughout the whole fibre felt whilst at the same time, owing to the temperature prevailing during pressing, it is exposed to an initial hardening. The final hardening is effected after accomplished pressing in hardening chambers at a temperature of, for example, 165 C., during a period of 6 to 9 hours.
The oil-tempered hardboard produced in the manner described above has a bending strength of 900-950 kg./ cm. and absorbs, after immersion in water at 25 C., for 6 hours 78%, for 24 hours 14-16%, and for 72 hours 21-24% of water.
Example 2 In this case the treatment is carried out as in Example 1 with the exception that the full pressure of 50 kg./cm. is only applied for one period of 30 to 45 seconds. The pressure is then decreased for boiling off water Whereupon the board thus treated is subjected to the heattreatment for final hardening, as indicated above.
v Example 3 In order to increase the strength of a standard wallboard material by 20% and improve its resistance to water an impregnation is carried out with an impregnating agent consisting of a tall oil product modified with maleic acid anhydride and esterified with glycerine and having a viscosity of 1000 to 2000 cps. at 20 C.
This oil is added in the form of an emulsion of oil in water with a concentration of 12% oil, When preparing the emulsion ammonia is added which with the free fatty acids of the tall oil product serves as the emulsifier. The emulsion is added in the same way as in Example 1, whereupon the fibre felt is subjected to pressure, likewise under the same conditions as in Example 1. In this case, however, the oil is not distributed homogeneously throughout the whole fibre mass but the content thereof decreases progressively through the fibre material towards the wire net side of the felt. With the form of impregnation carried out in this way a board product is obtained which has been found very suitable for treatment by painting, inasmuch as the impregnating medium affords good adhesion for the binding medium and also gives a reduced consumption of the latter.
When increasing the addition of the said impregnating agent to 2%, based on the dry weight of the fibre material, it is possible to improve further the strength properties of the board. Thus, in this'case, the bending strength is increased with 50 to 60%, in comparison with the original standard wallboard. 1
Example 4 In this case the treatment is carried out in the same way as in any of the previous examples, but as the impregnating agent is used a product obtained by modifying fatty acids from soya bean oil or comparable unsaturated fatty acids with maleic acid anhydr'ide esterified with glycerol.
Example 5 The treatment is carried out as in any of the Examples 1 to 3 but as the impregnating agent is employed blown linseed oil.
Example 6 The treatment is carried out as in any of the Examples 1 to 3 but as the impregnating agent is employed, alone or in admixture with a semidrying or a drying oil, melamine formaldehyde resin etherified with butanol, for example the product which is sold under the name Mepas.
Example 7 The treatment is carried out as in the previous example but as the impregnating agent is employed, alone or in admixture with a semidrying or a drying oil, urea formaldehyde plast etherified with butanol, for example the product sold under the name Karpas.
Example 8 In this case the treatment is carried out as in any of the Examples 1 to 3 but as the impregnating agent is employed, alone or in admixture with a semidrying or a drying oil, a phenol etherified with butanol, for example the product p-tertiary butyl phenol manufactured and sold by the Dow Chemical Company, Midland, Michigan, U. S. A.
Example 9 The treatment is carried out as in any of the Examples 1 to 3 but as the impregnating agent is used dehydrated castor oil.
Example 10 In this case the impregnation is carried out With menhaden oil. The disagreeable odour of this product disappears When the board material is subjected to the treatment for hardening.
Example 11 In this case the impregnation is carried out with a fat alkyd resin dissolved in a solvent, such as white spirit. In other respects the treatment is carried out as in any of the Examples 1 to 3. The solvent is removed in the pressing operation simultaneously with the water when boiling oif the latter.
Example 12 The treatment is carried out as in any of the foregoing examples, but in addition a siccative is added to the impregnating agent, such as an iron or a manganese naphtenate, in quantities of the order of magnitude of 0.1-1.0% metal based on the quantity of the impregnating agent.
Example 13 In this case the treatment is carried out as in any of the Examples 1 to 3 but as the impregnating agent is used blown tall oil, partly or completely esterified with a polyhydric alcohol, for example pentaerythrite. Owing to its own colour, this tall oil product imparts to board treated therewith a grey shade of colour.
Example 14 The treatment is carried out as in anyv of the previous examples, but in addition to the impregnating agent small amounts of tetra or pentachlor phenol, chlornaphtalins or salts of said compounds are added.
I claim: I
1. In the manufacture of cardboard, wallboard, chipboard and similar fiberboards wherein a wet felt is pressed under conditions of high pressure and high temperature against a polished plate on one of its faces only, the process of impregnating the fiberboard to increase its strength which consists essentially in applying to one face only of the wet felt, after it has been formed into a continuous fiber felt but before it has received its final form by hot pressing, an aqueous emulsion having water as the continuous phase and containing from about 0.1 to 12%, based on the dry weight of the felt, of an impregnating agent selected from the class consisting of thermoplastic and thermosetting materials, said impregnating agent having a viscosity within the range of from about 300 to 5000 centipoises at 20 C., the amount applied being suificient to cause impregnation of the felt in the amount of from about 0.1 to 12% by weight of the impregnating agent based on the weight of the dry felt, then pressing the so-impregnated felt between a polished plate facing the impregnated face of the felt and a screen facing the unimpregnated face, at a temperature within the range of from about to 220 C., and at a pressure within the range of from about 15 to SOkg-Jcm for a period of from about 6 to 20 minutes and simultaneously driving out the'water present in the resulting board partly in the form of steam through the non-impregnated face, whereby the impregnating agent is caused to penetrate to a substantial depth into the fiberboard; the impregnated face of the felt being made acid in reaction at least prior to completion of the said pressing step, whereby sticking of the felt to the polished plate is prevented; and then hardening the board by heating it.
2. The process of claim 1 wherein the impregnating agent consists of a product obtained by modifying unsaturated higher fatty acids with dienophil compound, and esterifying with a polyhydric alcohol.
3. The process of claim 1 wherein the impregnating agent is a product obtained by modifying tall oil with maleic acid anhydride and esterifying with glycerol.
4. The process of claim 1 wherein the impregnating agent is linseed stand oil.
5. The process of claim 1 wherein the impregnating agent is a urea formaldehyde resin etherified with alcohol, in admixture with a drying oil 6. The process of claim 1 wherein the impregnating agent is applied in the form of an aqueous emulsion containing an ammonium compound as emulsifying agent.
7. The process of claim 1 wherein the board is hardened by heating it in air to a temperature of from about 150 to 200 C. for from about 12 hours to 1 hour.
8. The process of claim 1 wherein the pressing operating includes at least one high-pressure treatment followed by decreasing the pressure to permit the water contained in the felt to escape.
9. The process of claim 1 wherein the impregnating agent has a viscosity within the range of from about 300 to 2000 centipoises at 20 C. and is applied in quantity insufiicient for complete impregnation of the board.
10. The process of claim 1 wherein the impregnating agent has a viscosity within the range of from about 2000 to 5000 centipoises at 20 C. and is applied in quantity sufficient for complete penetration of the impregnating agent into the board.
11. In the manufacture of cardboard, wallboard, chipboard and similar fiberboards wherein a wet felt is pressed at high pressure and temperature between a polished plate and a Wire net, the process of impregnating the fiberboard to increase its strength which consists essentially in applying to one face only of the wet felt, after it hasbeen formed into a continuous fiber felt but before it has received its final form by hot pressing,
an aqueous emulsion of tall oil modified with maleic acid anhydride and esterified with glycerol and having a viscosity within the range of from about 2000 to 5000 centipoises at 20 C., said aqueous emulsion having water as its continuous phase, the amount applied being suffi'cient to cause impregnation of the felt in the amount of from about-6 to 8% by weight of the impregnating agent based on the dryweight of the felt, then subjecting the so-impregnated felt to a pressing operation under a pressure of from about 15 to 50 l g./cm. at a temperature within the range of from about 130 to 220 C. between a polished plate facing the impregnated face of the felt and a wire mesh facing the unimpregnated face of the felt, thereby causing the impregnating agent to 8 flow into and distribute itself homogeneously in the felt; the impregnated side of the felt being made acid in reaction at least prior to completion of the pressing step, whereby sticking of the felt to the polished'plate is" prevented; the water present in the felt partly in the form of steam through the said wire mesh, then hardening the board by heating at a temperature within the range of from about 150 to 200 C.
12. In the manufacture of cardboard, wallboard, chipboard and' similar fiberboards wherein a wet felt is pressed at high pressure between a polished'plate and a wire net, the process of impregnating the fiberboard to increase its strength which consists essentially in applying to one face only of the wet felt, after it has been formed into a continuous fiber felt but before it has received its final form by hot pressing, an aqueous emulsion of tall oil modified with maleic acid anhydride and esterified with glycerol and having a viscosity within the range of from about 300 to 2000 centipoises at 20 C., the amount applied being sufficient to cause only partial impregnation of the felt with the impregnating agent, then pressing the so-impregnated felt between a polished plate facing the impregnated face of the felt and a wire mesh facing the unimpregnated face of the felt, at a temperature within-the range of from about 130 to 220 C. and at a pressure within the range of from about to 50 kg./cm. for a period of from about 6 to minutes while simultaneously removing the Water present in the felt partly in the form of steam through said-wire mesh, then hardening the board by heating it in the presence of air at a temperature withinthe range of from 7 about 150 to 200 C.
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