WO1991005813A1

WO1991005813A1 - Process for the production of a white fine-grained material of urea-formaldehyde resin or a modified urea-formaldehyde resin

Info

Publication number: WO1991005813A1
Application number: PCT/SE1990/000650
Authority: WO
Inventors: Stig Ohlsson
Original assignee: Perstorp Ab
Priority date: 1989-10-20
Filing date: 1990-10-10
Publication date: 1991-05-02
Also published as: AU6619790A; SE8903470D0; SE8903470L; SE464815B

Abstract

Process for the production of a white fine-grained material of urea-formaldehyde resin or a modified urea-formaldehyde resin. The process comprises reacting urea with formaldehyde at a molar ration of urea:formaldehyde between 1:0.4 and 1:2.5 at a temperature between 15 and 100 °C and at a pH between about 0.5 and 3.0, preferably between 0.8 and 2.0. Precipitated particles of urea resin being insoluble in the reaction mixture are then formed as a slurry.

Description

Process for the production of a white fine-grained material of urea-formaldehyde resin or a modified urea-formaldehyde resin

The present invention relates to a white fine-grained material of urea-formaldehyde resin or a modified urea-formaldehyde resin.

It is known before that urea-formaldehyde resins can be produced in many different ways and at different conditions depending on types of equipment and desired properties of the resin.

These known processes are directed towards a production of urea-formaldehyde resins or modifications thereof with the intention that the final use of the resin should be as a binding agent or as an agent for building up different structures, foam etc. by curing the resin by means of pH-reducing additives and/or heating.

At the production of conventional urea-formaldehyde resins a gel stage is passed during the different curing phases. This gel stage is very difficult to handle.

According to the present invention it has been possible to avoid the formation of a gel. Thus, a process for the production of a white fine-grained material of urea-formaldehyde resin or a modified urea-formaldehyde resin has been brought about. The process comprises reacting urea and formaldehyde in an aqueous solution at a molar ratio of urea*.formaldehyde between 1:0.4 and 1:2.5 at a temperature between 15°C and 100°C and at a pH between about 0.5 and 3.0, preferably between 0.8 and 2.0. Then precipitated particles of urea resin being insoluble in the reaction mixture are formed as a slurry. Suitably, this slurry is neutralized. Normally, there is a subsequent filtering step, where the particles are filtered off. Possibly, there are also further steps where the particles are washed with water and ground.

According to the invention the urea-formaldehyde resin or resin material is produced directly in an average particle size of about 10-60 micron.

The fine-grained urea-formaldehyde material can be used as an organic filler or whitening agent (colour pigment) in such connections where there is a demand thereof, for example at the production of white paper having good lithographic printing properties etc. Another field of use is as a fertilizer.

In order to get a suitable particle size of the urea-formaldehyde resin material a further fine grinding can be made by wet grinding or alternatively by dry grinding of a dried product.

According to one preferred embodiment of the invention the urea-formaldehyde resin is produced by adding a small amount of acid, for.example sulphuric acid to a heated aqueous solution of urea and mixing while stirring with a heated aqueous solution of formaldehyde. At the contact of the formaldehyde with the acidified urea solution, particles of urea resin which are insoluble in the water containing reaction mixture are rapidly precipitated. During the reaction heat is generated. Therefore, sometimes cooling is suitable. The resin in the particles contain a smaller or larger amount of cross linkings between the polymer chains depending on the reaction conditions. However, normally the resin can be regarded as cured.

When the whole amount of formaldehyde solution has been added the acid is suitably neutralized with alkali to a pH of 7 in such a manner that a water soluble salt is formed. The fine-grained urea-formaldehyde resin material is filtered and washed to remove salts and possible rests of the raw materials used. Then the resin is ready to be used. A further mechanical fine grinding may be necessary depending on the application.

The urea-formaldehyde resin can be produced by using a large number of variations such as different molar ratios, the concentration of the solutions used, acids or acid salts, neutralization agents and temperatures. According to one possible variation the slurry is not neutralized to a pH of 7 but to a lower pH such as 3-6.

Also direct modifications by addition of other reactants to the formaldehyde are also possible to achieve. Possible reactants are for example dicyandiamide, melamine, thiourea, benzoguanamine, aniline, phenol or alkylphenol. Of course, polymers of formaldehyde such as paraformaldehyde or other substances which can split off formaldehyde can be used instead of or as an addition to formaldehyde. Other suitable aldehydes are for instance acetaldehyde, iso-butyraldehyde, acrolein, crotonaldehyde, furfural and glyoxal. An addition of different surfactants and protective colloids can be used to influence for instance the size and the shape of the particles formed at the production. According to another embodiment of the invention, parts of the urea and formaldehyde used consist of a water soluble urea-formaldehyde precondensate, preferably produced by reaction of an aqueous solution of urea with an aqueous solution of formaldehyde at a molar ratio of urea:formaldehyde between 1:3 and 1:6 at a temperature of 15-100°C, preferably 70-100°C and at a pH of 0.5-5.

It is also possible that parts of the formaldehyde used are added as a melamine-formaldehyde precondensate or a melamine-urea-formaldehyde precondensate.

At all embodiments where a precondensate is used it is especially important to be observant of the reaction conditions to avoid a gel formation instead of the desired precipitation of resin particles. In order to avoid a gel formation the urea or melamine respectively in the precondensate should make a minor proportion of the total amount of urea. Preferably, the amount of urea or melamine respectively in the precondensate is at most 25%, preferably at most 15% of the total amount of urea at the production of the resin particles.

Preferably, the precipitation reaction is carried out at a molar ratio of urea:formaldehyde between 1:1.0 and 1:1.8. When the resin is used as a fertilizer the most preferred molar ratio is between 1:0.5-1:0.9.

Many different organic and inorganic acids can be used such as sulphuric acid, sulfamic acid and/or phenolsulfonic acid.

The precipitation temperature is preferably between 60 C and 100°C. The invention will be further illustrated in connection with the embodiment examples below, of which examples 1, 2, 3, 4, 6, 7, 8, 9, 10 and 11 show how the reaction conditions can be varied within the scope of the invention. Example 5 is a comparison test outside the scope of the invention with an unsuccessful result.

Example 1 (molar ratio 1:1)

In a glass flask 600 g urea, 600 g distilled water and 100 g 20 per cent sulphuric acid were mixed. The mixture was heated while stirring to about 70°C. Thereafter, 600 g of a 50 per cent aqueous solution of formaldehyde was added, which reacted with the acidified urea solution, whereby small particles of insoluble urea resin were formed quickly. Due to the generation of heat, cooling of the flask was necessary.

The content of urea resin particles in the flask was neutralized by addition of sodium hydroxide solution to a pH of about 7, whereupon the particles were filtered off and washed carefully with water.

The fine-grained material could be used directly as a water containing filler. Alternatively, the material can be fine ground for instance by wet grinding or by normal dry grinding after drying.

Example 2 (molar ratio 1:1.40)

570 g of a 50 per cent aqueous solution of formaldehyde and 30 g 50 per cent sulphuric acid were introduced into a glass flask. At the same time an aqueous urea solution consisting of 400 g urea and 935 g water was made ready. The aqueous urea solution was then charged while stirring into the flask at a temperature of 60-70°C, whereby a white precipitation was rapidly formed at generation of heat.

The precipitation formed did not have the same fine-grained nature.as in Example 1. Instead bigger lump formed particles could be present.

The content of suspended urea resin particles in the flask was neutralized to a. pH of 7 by addition of an aqueous solution of sodium hydroxide, whereupon the particles were filtered off and washed carefully with water.

After a wet grinding to a narrow and very small average particle size the material could be used as a white agent at the production of paper with equivalent properties as those obtained with other pigment materials such as kaolin present on the market.

Example 3 (molar ratio 1:0.4)

In a glass flask 600 g urea, 10 g phenolsulfonic acid and 325 g 20 per cent sulphuric acid were charged.

The mixture was heated to about 75°C while stirring. Thereafter, 240 g 50 per cent aqueous solution of formaldehyde was added, whereby a thick slurry of particles of cured resin was formed immediately. In order to get the content more fluent 600 g water was added.

The sludge was then neutralized with a sodium hydroxide solution to a pH of 7, whereupon the particles were filtered off and washed carefully with water.

Example 4

935 g distilled water, 401 g urea and 14.5 g concentrated sulphuric acid were charged into a glass flask at stirring.

The temperature was 18 C when the urea had been dissolved. Thereafter, 570 g 50 per cent aqueous formaldehyde solution was added. The temperature of the mixture then increased to 73 C. At the same time a white precipitation of cured urea resin was formed. In order to decrease the viscosity of the sludge another 200 g of water was added.

The slurry was neutralized to a pH of 7 with an aqueous solution of sodium hydroxide. The particles were filtered off and washed carefully with water, whereupn they could be used as a water containing filler.

Example 5 (molar ratio 1:1.42)

570 g 50 per cent aqueous solution of formaldehyde was charged into a glass flask while stirring. By means of a sodium hydroxide solution pH was adjusted to abut 8.5. Thereafter 190 g urea and 635 g distilled water were added. pH was then found to be 8.5. The mixture was heated to 60 C for two hours, whereupon the temperature was increased to 90°C. Then 211 g urea, 250 g distilled water and 70 g 20 per cent sulpuric acid were added. At the addition of the sulphuric acid the temperature increased to 98°C and within 5 minutes the content of the flask was a solid gel lump which made a stirring and further work such as neutralization of the sulphuric acid impossible. The content could not be used.

Example 6 (molar ratio 1:1.23)

In a reactor 590 kg urea, 1379 kg water and 100 kg 20 per cent sulphuric acid were mixed. The mixture was heated at stirring to 85°C. Then 770 kg 50 per cent aqueous solution of formaldehyde was added, which reacted with the acidifed urea solution, whereby small particles of insoluble urea resin were precipitated from the reaction mixture which had a pH of 1.3.

The content of urea resin particles in the reactor was neutralized by addition of sodium hydroxide solution to a pH of 7, whereupon the particles were filtered off and washed carefully with water.

The porous fine-grained material had a specific area of

2 about 30 m /g, an average particle size of 25 μm and a brightness of 95 (L value according to CIE-Lab 1964,

D65, 10 observer).

After a wet grinding in a pearl mill to an average particle size of 1-10 μm the material had a specific area of 32 m 2 and a pore volume of 1.16 cm3/g.

The fine-grained material can be used at the production of paper to increase the brightness and opacity values or the scattering coefficient. For instance a certain thermomechanical paper pulp had a scattering coefficient of 58-60 m 2/kg in newsprint paper. At the addition of 3 parts by weight of the above particles a scattering 2 coefficient of 64 m /kg was obtained and with 6 parts by

2 weight 69 m kg.

Example 7 (molar ratio 1:1.5)

In a glass flask 1000 g urea, 2300 g water and 50 g sulfamic acid were mixed. The mixture was heated to 70°c.

Thereafter 1500 g of a 50 per cent aqueous solution of formaldehyde was added, which reacted with the acidified urea solution, whereby small particles of insoluble urea resin were formed in the reaction mixture which had a pH of 1.1.

The mixture was neutralized, washed and filtered to a. white powder.

The appearance of the particles formed varied. However, they were all more or less porous. Some looked like a cluster of grapes and others were more rounded.

Example 8 (molar ratio 1:1_..17)

In a glass flask 1000 g urea, 2450 g water, 190 g 20 per cent sulphuric acid and 80 g melamine were mixed. The mixture was heated to 70°C.

Thereafter 1165 g 50 per cent aqueous solution of formaldehyde was added, which reacted with the acidified urea solution, whereby small particles of insoluble melamine modified urea resin were formed in the reaction mixture which had a pH of 1.5. The mixture was neutralized, washed and filtered to a white powder.

The appearance of the particles varied. However, they were all more or less porous. Some looked like a cluster of grapes and others were more rounded.

Example 9 (molar ratio 1:1.11)

In a glass flask 1050 g urea, 2450 g water, 190 g 20 per cent sulpuric acid and 10 g hydroxyethyl cellulose were mixed. The mixture was heated to 70 C.

Thereafter 1165 g 50 per cent aqueous solution of formaldehyde was added, which reacted with the acidified urea solution, whereby small particles of insoluble urea resin were formed in the reaction mixture, which had a pH of 1.0.

The mixture was neutralized, washed and filtered to a white powder.

The particles formed were rounded and porous.

Example 10 (molar ratio 1:1.11)

In a glass flask 1050 g urea, 2450 g wa er, 190 g 20 per cent sulphuric^" acid and 2 g of a cation active tenside of a quarternary amine type were mixed. The mixture was heated to 70°C.

Thereafter 1165 g 50 per cent aqueous solution of formaldehyde was added, which reacted with the acidified urea solution, whereby small particles of insoluble urea resin were formed in the reaction mixture, which had a pH of 1.2.

The mixture was neutralized, washed and filtered to a white powder.

The particles formed were porous and round or rounded.

Example 11 (molar ratio 1:1.11)

In a glass flask 100 g urea and 525 g of a 50 per cent aqueous formaldehyde solution were mixed. The mixture was heated to 85°C and it was allowed to precondensate at a pH of 3.0-4.5 for 1 hour.

To the above precondensate 2450 g water, 950 g urea and 190 g 20 per cent sulphuric acid were charged. At a temperature of 70°C, 640 g of a 50 per cent aqueous solution of formaldehyde was added,, which reacted with the acidified solution, whereby particles of insoluble urea resin were formed in the reaction mixture, which had a pH of 1.4.

The mixture was neutralized, washed and filtered to a white powder.

The particles were porous and round and could be wet ground to smaller grain sizes.

The invention is not limited to the embodiments shown, since these can be modified in different ways within the scope of the present invention.

Claims

CLAIMS .

1. Process for the production of a white fine-grained material of ure -formaldehyde resin or a modified urea-formaldehyde resin, which comprises reacting urea with formaldehyde in an aqueous solution at a molar ratio of urea:formaldehyde between 1:0.4 and 1:2.5 at a temperature between 15°C and 100°C and at a pH between about 0.5 and 3.0, preferably between 0.8 and 2.0, whereby precipitated particles of urea resin being insoluble in.the reaction mixture are formed as a slurry.

2. Process according to claim 1, wherein the reaction is carried out at a temperature between 60°C and 100°C.

3. Process according to claim 1, wherein the molar ratio urea:formaldehyde is 1:1.0-1:1.8.

4. Process according to any one of claims 1-3, wherein parts of the urea and formaldehyde used consist of a water soluble urea-formaldehyde precondensate produced by reaction of an aqueous solution of urea with an aqueous solution of formaldehyde at a molar ratio of urea:formaldehyde between 1:3 and 1:6 at a temperature of 15-100°C, preferably 70-100°C and a pH of 0.5-5.

5. Process according to any one of claims 1-3, wherein the whole amount of urea and formaldehyde is present as aqueous solutions which are mixed with each other.