DE2332046A1 - Melamine/formaldehyde acidic colloidal soln. prepn. - storage stable, used in paper prodn. to increase wet strength - Google Patents

Abstract

The process comprises precondensing melamine and HCHO (or a cpd forming HCHO) in an aqs. suspension at pH 4-9; followed by treatin gthe precondensate with excess HCHO in above pH range and finally acidifying the condensate suspension with HCl or an aliphatic carboxylic acid with apKa =3.5 and/or phosphoric acid. The soln. is storage stable for >=6 months without gelling and when incorporated in paper gives a prod. with superior wet strength than when prior art resins (as prepd by US 2986489) are used.

Description

Our reference: O.Z. 29 950 Ze / Ws

6700 Ludwigshafen, June 22nd, 1973

Process for the preparation of acidic colloidal solutions of melamine-formaldehyde resins

Addendum to patent (patent application P 22 41 713.6)

Subject of the German patent (patent application

P 22 4l 713.6) is a process for the production of acidic colloidal Solutions of melamine-formaldehyde resins by reacting melamine and formaldehyde or at least one formaldehyde outgoing compound in the aqueous phase, treatment of the resulting precondensate with further formaldehyde and then Aging of the solution at pH values <5, using melamine and formaldehyde or at least one formaldehyde-releasing compound initially precondensed in aqueous suspension at pH values between 4 and 9, the precondensate with further formaldehyde aftertreated under the stated pH conditions and the condensate suspension then with hydrochloric acid and / or phosphoric acid pissed off. It has now been found that the method in terms of its implementation and in terms of the receiving Colloidal solutions can be improved if at least one aliphatic acid is used instead of hydrochloric acid Carboxylic acid, which has a pK value of = 3.5, is used.

As aliphatic carboxylic acids in the context of the invention it is expedient to use those which are still water-soluble, e.g. those with 1 to 4 carbon atoms, such as formic, acetic, propionic or butyric acid. However, formic acid is preferably used .

The modified process can be implemented according to the provisions of the main patent in such a way that melamine is also used initially with formaldehyde or formaldehyde-supplying compounds,

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expediently with 10 to 40 # aqueous formaldehyde solutions and preferably a 25 to 30 # formaldehyde solution, in a molar ratio of 1.5 to 5> preferably 3 * 2 mol of formaldehyde per mol of melamine, slurried with water. The mixture is then generally uniformly within 10 to 90, preferably about 20 to 40 minutes, to produce a solution at self-adjusting pH values between 4 and 9, mostly to temperatures between 50 and 100, preferably 60 to 80 ° C and then generally 0.1 to 2.5 hours, in particular 1/2 to 1/2 hours, mostly 50 to 100, preferably about 6o to 80 ° C condensed. A 10 to 40, preferably approx. 20 to 25, aqueous formaldehyde solution is then added to achieve a final molar ratio of, for example, 5 to 20, preferably 9 to 14 mol of formaldehyde per mol of bound melamine, thereby interrupting the condensation and cools the solution down intensively. After usually 0.2 to 4, preferably 1 to 1/2 hours, the temperature is generally increased to 25 to 50, preferably 25 to 30 ^° C., and so much of the corresponding carboxylic acid according to the definition is added that it has a molar ratio of 0.1 to 0.8, preferably 0.2 to 0.5 mol of anhydrous acid, or together carboxylic acid and phosphoric acid, advantageously as an 85% solution, in the specified molar ratios per mol of bound melamine with a molar ratio preferably above 0.2, in particular 0, 4 to 0.8 moles of carboxylic acid per mole of phosphoric acid, preferably with intensive mechanical agitation, into the solution and then preferably immediately diluted with water from a temperature below 70 ^° C., preferably 25 ^° C., to a concentration that has a dry content of the solution of usually corresponds to 6 to 15, preferably approx. 10 to 15 %. The solution is then allowed to age.

The reaction conditions of the modified process are practically the same as in the process of the main patent. Man condenses in the weakly acidic to weakly alkaline pH range, preferably in compliance with special conditions Concentration, temperature, molar ratio and reaction time in

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two stages with formaldehyde or formaldehyde-supplying compound. Subsequently, after a specially defined cooling phase in a certain temperature range, a carboxylic acid expediently given in amount and composition is added, or the mixture of carboxylic acid with phosphoric acid, then diluted with water to a resin solids content, as is also described in US Pat. No. 2,986,489 , and ages in a similar way. The solution produced by the modified process now generally has a pH between 1.7 and 3> 5. The formation of a colloidal state, recognizable by a bluish Tyndall effect, is only slightly pronounced in this pail after standing for 30 hours at room temperature, but the pH value changes to values between 1.5 and 2.2 during this time and remains then constant. The clear solutions obtained, with at most a slight whitish-bluish tinge, remain ^{low-viscosity for at least 8 to 10 months without gelling when stored below 25 °} C., ie the stabilizing effect is increased compared to the process according to the main patent. Only after a period of more than 12 months does the viscosity gradually increase up to the gelling point.

The solutions obtained by the modified process are also excellent tools for increasing the wet strength effect in the manufacture of paper. The effect of increasing the wet strength effect of paper is when resin is used according to the modified process once considerably larger than with the resins of the prior art and compared with the resins of the Main patent also improved significantly.

The following examples explain the modification according to the invention of the procedure.

example 1

To produce the resin, 3 * 2 are placed per mole of melamine powder Mol 27 #igen formaldehyde in a stirred tank and heated

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233/046

after filling of the melamine within 25 min. at 65 ⁰ C uniformly, thereby forming in the pH range 4-9 without particular setting a clear solution. This temperature is now maintained for 1 hour, effective cooling is then set and at the same time 6.7 moles of a 25% formaldehyde are topped up. After about 40 min. To be reached a temperature of 3O ⁰ C in the solution. The cooling is now stopped and 0.21 moles of 85% formic acid, 0.26 moles of 80% phosphoric acid and 56 moles of drinking water at a temperature below 25 ° C. are poured in one after the other. A colorless, still clear solution with a pH of 2.8 is obtained. About 12 hours after production, the resin has the following properties:

Appearance: Transparent yet clear, in great thicknesses

slightly bluish solution. Density 1.07 kilograms per liter at 20 ⁰ C pH: 2.0 with no further change dry residue after 2 hours at 120 ⁰ C. 12.3 percent by weight viscosity at 20 ⁰ C by Hoppler: 4.9 mPa.s Shelf life at 25 ° C without gelling: 6 months wet-strengthening effect of paper according to the measurement method specified in the patent OZ 29 356 (patent application P 22 41 713.6) in Example 1 as "wet tear length in m" with and without "artificial aging".

Papermaking NRL (m)
unaged NRL (m)
aged without the addition of melamine resin 60 90 3 % addition of melamine resin as
1 # solution 555 880 6 % addition of melamine resin as
1 $ solution 800 1105

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Example 2

A resin with the same type is obtained when 3> 2 moles of 30 #igen formaldehyde initially taken in a stirred tank per mole MeIaminpulver, after filling of the melamine over 40 minutes even at 70 ⁰ C is heated, whereby, at a pH value of 6 8 forms a clear solution without any special adjustment, maintains it for 45 minutes at this temperature, then sets effective cooling and at the same time refills 6.7 moles of a 23 # formaldehyde and after 30 minutes at a measured temperature of 25 ° C without cooling one after the other 0 , 15 moles of 85 # formic acid, 0.33 moles of 80 # phosphoric acid and 58 moles of drinking water at a temperature of 22 ° C. The pH value of the colorless and clear solution obtained in this way is initially 2.7, after 12 hours the resin has the following properties:

Appearance: Transparent, still clear, in large layers

bluish

Density: 1.071 kg per liter at 20 ⁰ C pH: 1.85 without further modification dry residue after 2 hours at 120 ⁰ C: 12.1 wt .- ^ viscosity at 20 ° C according to Hoppler: 6.4 mPa.s Shelf life at 25 ° C without gelling: 5 months wet strength effect of paper

NRL (m) NRL (m) paper manufacture unaged aged

without the addition of melamine resin 55 80

3 % resin addition as a 1 # solution 570 875

6 # resin addition as 1 # solution 775 1115

Example 3

Another resin of the same type is obtained if 3.2 moles of 25% formaldehyde are added per mole of melamine powder in a stirred tank submitted, heated uniformly to 60 ° C within 20 minutes after filling in the melamine, with a pH of

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7.1 forms a clear solution without any special adjustment, maintains it at this temperature for 90 minutes, then sets effective cooling and at the same time it was topped up with 6.7 moles of a 26% formaldehyde and after 60 minutes at a temperature that was now measured from 28 C without further cooling successively 0.18 moles 85 $ Formic acid, 0.27 moles of 80% phosphoric acid, and 58 moles of drinking water at a temperature of 26 ° C. The pH of the colorless and clear solution obtained in this way is initially around 2.5, after 12 hours the resin has the following properties:

Appearance: Transparent, still clear, in great thicknesses

bluish

Density: 1.069 kg per liter at 20 ⁰ C pH: 1.92 without further modification dry residue after 2 h 120 ⁰ C:.. 11.9 wt # Höppler viscosity at 20 ⁰ C: 5.2 mPa.s storability at 25 ° C without gelling: 6 months wet strength effect of paper

NRL (m) NRL (m) paper manufacture unaged aged

without addition of melamine resin 60 85

J5 % resin addition as 1 # solution 585 900 6 % resin addition as 1 # solution 750 1175

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Claims (2)

- 7 - O.Z. 29 950 Claims Modification of the process for the production of acidic colloidal solutions of melamine-formaldehyde resins by reacting melamine and formaldehyde or at least one formaldehyde-releasing compound in the aqueous phase, treating the resulting precondensate with further formaldehyde and subsequent aging of the solution at pH values <5, whereby melamine and formaldehyde are used or at least one formaldehyde-releasing compound is first precondensed in aqueous suspension at pH values between 4 and 9, the precondensate is aftertreated with further formaldehyde at the stated pH conditions and the condensate suspension is then acidified with hydrochloric acid and / or phosphoric acid, according to patent (patent application P 22 713.6 4l), characterized in that for the acidification instead of hydrochloric acid, at least one aliphatic carboxylic acid which has a pK of = 3 * 5 is used. 2) Process according to claim 1, characterized in that the carboxylic acid is used as a mixture with phosphoric acid. Badische Anilin- & Soda-Fabrik AG V ^ _x 409884/1215 ORIGINAL INSPECTED