US2721505A - Process of spray coating a web and heating the coated surface - Google Patents

Description

United States Patent Ofiice Patented Oct. 25, 1955 PROCESS OF SPRAY COATING A WEB AND HEATING THE COATED SURFACE Bengt Johan Yngve Mossberg, Djnrsholm, Sweden, assignor to Aktiebolaget Statens Skogsindustrier, Stockholm, Sweden, a company of Sweden No Drawing. Application December 4, 1951, Serial No. 259,880

Claims priority, application Sweden December 8, 1950 21 Claims. (Cl. 92-40) This invention relates to improvements in processes for the manufacture of impregnated, pressed fibrous board materials, such as cardboard, wallboard, chipboard or the like (panels) provided with a coloured surface.

The invention is particularly adapted to be applied in connection with the process for producing such impregnated fibrous materials described in the copending application Serial No. 234,918, filed July 2, 1951. According to the process disclosed in said application the impregnating agent is supplied to the fibrous material when the latter already forms a continuous fibre felt but before it has received its final form by pressing under high pressure, by applying the impregnating agent to one side of the fibre felt. The felt is then subjected to a pressing at increased temperature under high pressure against a polished plate, or between a polished plate and a wire net, with the side of the felt provided with the impregnated agent turned against the polished plate. By this hot-pressing the impregnating agent is caused to flow and penetrate into and according to the quantity and viscosity thereof-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 water present in the felt through the side thereof turned away from the polished plate. Finally, the board thus treated is subjected to a hardening at increased temperature.

The impregnating agent used in this process may consist of synthetic resins both of a thermoplastic character, such as polyvinyl chloride, and of a thermosetting character, such as amino-plastics, phenolic-plastics, alkyd resins, and further, of raw or treated linseed oil, soya bean oil, tall oil or the like or compounds or combinations of the above orsimilar substances.

The present invention relates to a further development of this process and has for its object the production of similar entirely or partially impregnated, pressed fibrous materials (panels) which-are provided onone side with a layer of colour penetrating more or less deeply into the fibrous material and forming a complete or partial cover thereon, according to desire. The process of the invention is mainly characterized therein that simultaneously with the addition of the impregnating agent, or subsequently in connection therewith, a colouring agent is applied to the side of the fibre felt turned towards the polished plate. As colouring agent, any suitable inorganic or organic colour, preferably a pigment, may be employed.

It is already known, in the impregnation of fibrous materials after the latter has received its final form, to dip the fibrous material into the impregnating agent or a solution thereof mixed with pigment and thus obtain impregnated board of a certain colour. However, this process possesses many disadvantages. Owing to the fact that the impregnating agent runs off after dipping, the surface of, the fibrous material will present a less attractive appearance and moreover, the costs are high, since the consumption of the colouring agent and the impregnating agent is considerable.

It is also known to provide the fibrous material after it has been pressed and cut, with a layer of colour or coloured enamel. As example of such products obtained by surface treatment of the fibrous material after it has passed through the manufacturing process as a whole, may be mentioned so-called lacquer board. Such surface treatment is expensive, however, as it entails much work and requires considerable space. Products hitherto produced in this manner further have the disadvantage that the board panels, if exposed to water, have a tendency to swell to such an extent that the layer of lacquer cracks.

The disadvantages referred to above are eliminated according to the present invention which, both from a technical and economic point of view, offers a satisfactory solution of the problem of simultaneously impregnating a fibrous material and providing one side of it with a layer of colour varying in covering power, colour, gloss etc. for different requirements.

When applying the invention in practice, the impregnation of the fibrous material is carried out as described in said above mentioned copending application Serial No. 234,918. In accordance therewith it is preferred to use impregnating agents consisting of products of unsaturated higher fatty acidsor oils containing such fatty acids or resin acids, such as linseed oil, soya bean oil, tall oil and the likemodified 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 obtained from tall oil by modifying it with maleic acid anhydride 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.

Other suitable examples of impregnating agents are linseed stand oil, phenol formaldehyde resins and urea formaldehyde resins, the two latter preferably in state of oil-modified products, and alkyd resins.

It has been found suitable to employ an impregnating agent having a viscosity of from about 2000 to 5000 cps. at 20 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.

As examples of suitable colours may be mentioned the following white and coloured pigments: Zinc oxide, zinc sulfide, titanium dioxide, lithopone, antimony trioxide, barium sulfate, basic lead sulfate, yellow iron oxide, red iron oxide, brown iron oxide, black iron oxide, yellow cadmium sulfide, red cadmium sulfide, chrome yellow, chrome green, chrome red, chromium oxide, iron blue, cobalt blue, cobalt green, carbon black.

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.

The colouring agent may be added together with the impregnating agent, for example dissolved or dispersed therein, or in the vehicle in which the impregnating agent itself is supplied. The colouring agent may also be added separately, either as such in a dry condition or in the form of a suspension or solution.

According to the nature of the impregnating agent and the colouring agent, the manner in which they are added, the sequence in which this takes place and other working conditions, it is possible during the subsequent pressing operation against the polished plate to cause the impregnating agent and the colouring agent to penetrate to varying depths into the fibrous material. By suitable choice of the colouring agent and the impregnating agent and the conditions for their application it is thus possible to obtain, for example, a distribution of the impregnating agent in fibre felt throughout its entire thickness or only to a limited depth therein while the colouring agent is mainly concentrated on the surface, or in the surface layer, of the fibre felt which is turned towards the polished plate.

In cases where it is desired to obtain complete covering, relatively high contents of the colouring agent and the impregnating agent will be required owing to the fact that the colouring agent in a highly concentrated form sinks relatively deeply into the wet fibre felt.

According to a preferred form of the invention it has been found that the covering capacity of a pigment can be considerably increased if in addition to the pigment, an inorganic compound with such surface-active properties is added that it can serve as an interface active substance between the impregnating agent and water with water as the continuous phase, thereby facilitating the wetting of the colouring agent by the impregnating agent. In this way the colouring agent can be concentrated at the surface of the fibrous material, which allows complete covering to be obtained with a considerably lower colour content than is possible without such addition of an interface active substance. This is of particular importance in the case of White and light-shaded colouring agents.

As examples of such interface active substances may be mentioned silicic acid, silicates and aluminium hydroxides which may be used separately or in combination with each other in quantities within the ranges of 0.2 2.0%, for example, preferably 05-20%. They may either be added together with the colouring agent, for example in the form of a suspension, or separately.

By varying the amount of the additions of colouring agent and interface active substance, the covering properties of the colouring agent can be varied and a fibrous material with a coloured surface can thus be produced possessing diiferent qualities. The surface-hardness, re sistance to wear and other similar properties of the colour layer depend to great extent upon the choice of the impregnating agent and the method of applying the impregnating agent and the colouring agent. Thus, the process permits ample possibilities for variation, inasmuch as the addition of both the impregnating agent and the colour can take place successively in a number of stages, in such a way, for example, that impregnation is first carried out with an impregnating agent of relatively low viscosity which penetrates relatively easily into the fibrous material, and subsequently an impregnating agent having a higher viscosity, combined with the addition of the colouring agent, whereby great surface hardness is obtained.

When employing a suspension or emulsion of the colouring agent and the impregnating agent in water, it is necessary to work with a pH below 8 or in the presence of a salt which is decomposed during the pressing operation, while liberating an acid; otherwise adhesion of the fibrous material to the polished plate will occur.

The colouring agent may be added in quantities of llO%, for example, suitably l-8%, preferably 26%, based on the dry weight of the fibrous material. If desired, two or more difierent colouring agents may be added, for example a white pigment in combination with a coloured pigment in order to obtain different shades of colour.

After applying the impregnating agent and the colouring agent to the fibrous felt, the latter is subjected to a hot-pressing operation, as indicated above. Said pressing operation is preferably carried out in one or more periods of at least 3045 seconds at a full pressure of l5-50 kg./cm. at a temperature within the range of about 220 C., the total period of pressing varying from about 620 minutes depending on the temperature and pressure conditions used and the properties of the fibre material. The final hardening of the impregnated and pressed board material thus treated is then preferably effected by heating to a temperature of about 200 C., for 9-10 hours at the lower temperatures within said range, down to about 1 hour at a higher temperature in the neighbourhood of 200 C.

The coloured surface of .the board panels produced according to the present invention has the appearance of an enamel surface and is entirely smooth in distinction to the result obtained when enamelling in the ordinary manner, since the latter process can only be carried out by the application of several surface coatings with intermediate grinding of the surface. When the fibrous material is subjected to heat-hardening under pressure, or after the pressing operation, simultaneously a hardening of the colour layer is obtained.

The process according to the invention is extremely simple to carry out as it only forms a part of a completely automatic manufacturing process which does not require any extra space over what is necessary for the production of the fibrous material itself. The amount of extra work required and the consumption of colour and impregnating agent are low. Owing to the treatment to which the impregnating agent with the colouring agent is subjected during the pressing and heat-hardening operations, it is possible to employ cheaper compounds as impregnating agent than the type of binders which are necessary in the known manufacturing processes referred to above.

Example 1 In the production of wallboard provided with a whiteenamelled surface, the colouring agent and the impregnating agent are applied to the upper side of the fibre felt which, during subsequent pressing in the high-pressure press, is turned towards the polished plate at a point immediately following the last pair of rolls of the board machine. As white pigment, zinc oxide is employed in a quantity of 2-10% of the dry weight of the fibre, depending upon the degree of complete cover it is desired to obtain. As binding and impregnating agent. a tall oil product modified with maleic acid anhydride and esterified with glycerine or pentaerythritol is preferably employed. It is preferred to carry out the addition in two stages immediately following one another, and hereby in the second stage a binding medium such as a quickdrying alkyd is used, preferably a modified tall oil, for the purpose of obtaining a good wearing surface. For complete impregnation a quantity of oil of 610% is required, based on the dry weight of the fibre, depending on the content of pigment used. As additional substance, silicic acid and zinc silicate are preferably employed in a total amount of 12% of the dry weight of the fibre.

The pigment and the impregnating agent are added in the form of an emulsion of oil in water in a concentration of 1 part oil to 7 parts water. When preparing the emulsion, alkali silicate is added and is subsequently precipitated by addition of a metal salt and ammonium sulphate. The ammonium sulphate addition amounts to 0.5l.0% of the dry weight of the fibre. The pH of the emulsion should not exceed 6. It is essential to use a salt which is decomposed under the conditions of pressure prevailing, thereby producing permanent acid reaction in the water present in the fibre felt. The emulsion is applied from a spraying tube provided with nozzles, whereby a perfectly ever: surface coating is obtained on the felt.

After adding the emulsion, the fibre felt is transported into a high-pressure press where pressing takes place at a pressure of 50 kg./cm. at temperature of l90-200 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 and the residual water in the fibre felt is allowed to boil off. The total pressing cycle can hereby be varied within certain limits depending upon the quality of board required.

After pressing, the board panels are subjected to a heat treatment. It is preferred to carry out the first part of the hardening at a temperature at which the wood fibre will not undergo any reaction but during which hardening of the colour layer is completed, so that the second part of the heat treatment can be carried out at the temperature customary for board material.

The board panels produced in the manner described have a bending strength of 9001000 kg./cm. and absorb-after immersion in water at C. for 6 hours 78%, for 24 hours l416%, and for 72 hours 2l24% of water.

Example 2 The addition of pigment and silicic acid compound can also be carried out in the following manner: The fibre felt is coated with an oil emulsion containing silicic acid or a silicate in a finely divided form. Immediately afterwards the pigment-for example titanium dioxide in a quantity of 46%, based on the weight of the dry fibrous materialis added, together with further binding agent as stated in Example 1 in the form of an emulsion in water and preferably together with small quantities of silicic acid or a compound of the same. addition of silicic acid or silicate in the first mentioned coating stage, the degree of cover can be varied to a great extent when adding the pigment during the coating in the second stage. Pressing and hardening is carried out as in Example 1.

Example 3 For producing wallboard having a surface provided with a layer of colour, the colouring agent and the impregnating agent are applied to the upper side of the fibre felt in the same way as in Example 1. As pigment, such materials are preferably used which are stable at temperatures up to 200 C., for example lithopone.

The quantity of pigment required amounts to 26% of the dry weight of the fibre, depending upon the degree of cover it is desired to obtain. For complete impregnation a quantity of oil of 610% is required, based on the dry weight of the fibre, the amount depending upon the content of pigment. According to the degree of penetration of the pigment into the board which it is desired to attain, an addition of up to 0.5% silicic acid, based on the weight of the fibre, is employed.

The pigment and the impregnating agent are applied in the form of an emulsion of oil in water in a concentration of 1 part oil to 7 parts water. In case of using silicic acid it is added in the form of an alkali silicate which is subsequently precipitated by addition of ammonium sulphate, for example. The ammonium sulphate addition amounts to 0.540% of the dry weight of the fibre, but may be advantageously reduced in comparison with Example 1. The pH of the emulsion should not exceed 6. Also in this case it is essential that the water present in the fibre felt should have an acid reaction under the conditions prevailing during pressing. In other respects the treatment is carried out in accordance with the description in Example 1.

Example 4 In this case the impregnating agentlinseed stand oil,

By varying the soya bean oil, or alkyd resin, for example--is added in a quantity of 6-8% based on the dry weight of the fibre, in the form of an aqueous emulsion. Immediately afterwards, the pigment is applied to the upper side of the fibre felt mixed into a binding agent diluted with a solvent. By way of example, 68% of pigment, based on the dry weight of the fibre, may be added admixed with equal parts of the binding agent and a solvent.

After the additions have been made, the fibre felt is transported into a high-pressure press where it is subjected to pressure at 50 kg./cm. at a temperature of 190200 C. similarly as described in Example 1.

After pressing, the board panels are subjected to heathardening in the customary manner.

Example 5 In this case a colouring agent consisting of 4-6% of zinc oxide, titanium dioxide or lithopone and /2% of yellow iron oxide was added in order to obtain a colour with a yellow shade. In other respects the treatment was carried out as in any of the previous examples.

It may be mentioned that the term coloured used in the present application is intended to include also the case where only White colours are used.

I claim:

1. In the manufacture of impregnated cardboard, wallboard, chipboard and similar pressed fibrous board materials with a coloured surface, the process of adding an impregnating agent and a colouring agent to a watercontaining fibrous material after it has been formed into a continuous fibre felt but before it receives its final form by hot pressing by spraying said agents on one side only of the fibre felt, then subjecting the felt to a pressing operation under high pressure in the presence of heat against a polished plate with the impregnated side of the felt turned against the plate, this side of the felt being made acid in reaction at least prior to completion of the pressing step, whereby the impregnating agent and the colouring agent are caused to penetrate into and become homogeneously distributed in the fibre felt at least to a limited depth of the same without the felt adhering to the polished plate, at the same time forcing out water present in the felt through the side of the latter turned away from the polished plate, and then subjecting the board thus obtained to a hardening at a temperature of from about to 200 C.

2. The process of claim 1, in which the impregnating agent is a product obtained by modifying unsaturated higher fatty acids with a dionophil compound and esterifying with a polyhydric alcohol.

3. The process of claim 2, in which the impregnating agent is a tall oil product modified with maleic acid anhydride and esterified with glycerol.

4. The process of claim 1, in which the impregnating agent is an alkyd resin.

5. The process of claim 1, in which the impregnating agent is linseed stand oil.

6. The process of claim 1, in which the impregnating agent is soya bean oil.

7. The process of claim 1, in which the impregnating agent is added in consecutive steps.

8. The process of claim 1, in which impregnating agents are added in two consecutive steps, in the first step a tall oil product modified with maleic acid anhydride and esterified with a polyhydric alcohol and in the second step an alkyd resin.

9. The process of claim 1, in which the impregnating agent is added in a quantity of 68%, based on the dry weight of the fibrous material.

10. The process of claim 1, in which the colouring agent is a pigment.

11. The process of claim 1, in which the colouring agent is a pigment which is added in a quantity of l-10%, based on the weight of the fibrous material.

12. The process of claim 1, in which the impregnating 7 agent is applied in the form of an aqueous emulsion containing ammonium compounds as emulsifying agents and having suspended therein a pigment.

13. The process of claim 1, in which the impregnatin agent and the colouring agent are added in consecutive ste 5.

$4. The process of claim 1, in which a white pigment is added in a quantity of 1-8%, based on the dry weight of the fibrous material.

15. The process of claim 1, in which a white pigment in a quantity of 46%, based on the dry weight of the fibrous material, is added in combination with a small quantity of a coloured pigment, in order to impart a certain shade of colour to the board material.

16. The process of claim 1, in which the hot-pressing is carried out under a pressure of 50 kg./cm. at a temperature within the range of 130-220 C. and the hardening is accomplished in the presence of air at a temperature within the range of 150200 C.

17. The process of claim 1 wherein the coloring agent is a pigment and a surface-active agent is added to increase the covering power of the pigment.

18. The process of claim 17 wherein the surface-active agent is selected from a class consisting of silicic acid, zinc silicate and aluminum hydroxide, this agent being added in the amount of from about 0.2 to 2 per cent based on the dry weight of the fibrous material.

19. In the manufacture of impregnated and colored cardboard, wallboard, chipboard and similar pressed fiberboards, the process which comprises spraying one face only of a water-containing fibrous web, after it has been formed into a continuous fiber felt but before it has received its final hot pressing, with an aqueous emulsion of an impregnating agent having a viscosity within the range of from about 300 to 5000 centipoises and being selected from the class consisting of thermoplastic and thermosetting materials, said aqueous emulsion having water as its continuous phase and containing in suspension from about 2 to 6% of a solid coloring agent and from about 0.5 to 2% of a surface active agent serving to cause wetting of the coloring by said impregnating agent, the amount of aqueous emulsion applied being sutficient to penetrate the fibrous web to a substantial degree, then subjecting the so-impregnated web to a pressing operation under high pressure in the presence of heat between a polished plate and a wire screen with the impregnated side of the felt facing the plate, whereby the impregnating agent and the coloring agent are caused to 0 penetrate into and become homogeneously distributed in the fiber felt at least to a substantial depth of the same, at the same time forcing out the water present in the felt through the side of the latter facing the wire screen, and then subjecting the board thus obtained to heat hardening at a temperature of from about to 200 C. 20. The process of claim 19 wherein the impregnating agent has a viscosity within the range of from about 2000 to 5000 centipoises and substantially complete impregnation of the felt is thereby obtained.

21. The process of claim 19 wherein the impregnating agent has a viscosity within the range of from about 300 to 2000 centipoises and only partial impregnation of the felt is produced.

References Cited in the file of this patent UNITED STATES PATENTS Re. 19,187 Obedorfer May 29, 1934 443,658 Carpenter Dec. 30, 1890 1,829,187 Piessevaux Oct. 27, 1931 1,941,536 Boehm Jan. 2, 1934 1,957,370 Thomas et al. May 1, 1934 2,030,625 Ellis Feb. 11, 1936 2,060,824 Rafton Nov. 17, 1936 2,078,272 Novak Apr. 27, 1937 2,081,889 Borglin May 25, 1937 2,208,236 Wiener July 16, 1940 2,208,511 Ellis July 16, 1940 2,229,620 Bradner Jan. 21, 1941 2,304,818 Grupe Dec. 15, 1942 2,304,819 Grupe Dec. 15, 1942 2,315,675 Trommsdortf Apr. 6, 1943 2,325,302 Britt July 27, 1943 2,373,914 Quinn Apr. 17, 1945 2,378,113 Von De Carr June 12, 1945 FOREIGN PATENTS 30,217 Austria Oct. 10, 1907 25,451 Netherlands Dec. 15, 1931 OTHER REFERENCES Manufacture of Pulp and Paper, 3rd ed., vol. IV, Sec. 5, pages 28 and 29, Sec. 6, pages 7, 10, 15 and 63 (1937); vol. V, Sec. 4, pages 12, 14, 21, 31 and 38 (1939). Published by McGraw Hill, New York.

Collins, Paper Ind. and Paper World, June 1943, page 266.

Claims (1)

1. IN THE MANUFACTURE OF IMPREGNATED CARDBOARD, WALLBOARD, CHIPBOARD AND SIMILAR PRESSE D FIBROUS BOARD MATERIALS WITH A COLOURED SURFACE, THE PROCESS OF ADDING AN IMPREGNATING AGENT AND A COLOURING AGENT TO A WATERCONTAINING FIBROUS MATERIAL AFTER IT HAS BEEN FORMED INTO A CONTINUOUS FIBRE FELT BUT BEFORE IT RECEIVES ITS FINAL FORM BY HOT PRESSING BY SPRAYING SAID AGENTS ON ONE SIDE ONLY OF THE FIBRE FELT, THEN SUBJECTING THE FELT TO A PRESSING OPERATION UNDER HIGH PRESSURE IN THE PRESENCE OF HEAT AGAINST A POLISHED PLATE WITH THE IMPREGNATED SIDE OF THE FELT TURNED AGAINST THE PLATE, THIS SIDE OF THE FELT BEING MADE ACID IN REACTION AT LEAST PRIOR TO COMPLETION OF THE PRESSING STEP, WHEREBY THE IMPREGNATING AGENT AND THE COLOURING AGENT ARE CAUSED TO PENETRATE INTO AND BECOME HOMOGENEOUSLY DISTRIBUTED IN THE FIBRE FELT AT LEAST TO A LIMITED DEPTH OF THE SAME WITHOUT THE FELT ADHERING TO THE POLISHED PLATE, AT THE SAME TIME FORCNG OUT WATER PRESENT IN THE FELT THROUGH THE SIDE OF THE LATTER TURNED AWAY FROM THE POLISHED PLATE, AND THEN SUBJECTING THE BOARD THUS OBTAINED TO A HARDENING AT A TEMPERATURE OF FROM ABOUT 150* TO 200* C.