CS203735B1 - Process for preparing aqueous solutions of phenolformaldehyde resins of phenolic type - Google Patents

Description

The present invention relates to a process for the preparation of aqueous solutions of phenol-formaldehyde resols, particularly suitable for impregnating cellulosic materials in the production of molded laminates and molding films.

Aqueous solutions of phenol-formaldehyde resole resins have a very wide range of applications. They are prepared for individual applications with different concentrations, different viscosities and different reaction properties. Phenolic resole resins are formed by reaction of phenol with formaldehyde in an alkaline medium. In the first reaction stage, formaldehyde is added to phenol to form phenolalcobols (methylphenols), which in the next stage react with each other to form polynuclear compounds containing reactive methylol groups which cause resin hardenability. By varying the reaction conditions in the preparation of the resole resins, various product properties can be achieved. For example, depending on the type and amount of alkaline catalyst used, the water product may be more or less soluble in water, the amount of reactive methylol groups in the reaction product depends on the formaldehyde content of the reaction mixture and thus the degree of reactivity of the resin. the molecular weight of the reaction product, respectively. its viscosity, the degree of dewatering the final product can be adjusted to the required resin concentration.

The reaction catalysts used in the preparation of water-soluble resols are most often alkali metal hydroxides, in particular NaOH and KOH, or their carbonates or sulphites, and caustic earth metal hydroxides or oxides, in particular Ca (OH) 2, Ba (OH) 2, CaO, MgO.

The molar ratio of phenol to formaldehyde used ranges from 1: 1.1 to 1: 3. For low molecular weight products of low viscosity, which are widely diluted with water, a high molar excess of formaldehyde is applied, For higher molecular weight resols of higher viscosity and with limited miscibility with water, prepared usually at higher concentrations, a molar excess of formaldehyde is used less. The smaller the molar excess of formaldehyde, the higher the free unreacted phenol content of the final product is generally. The curable resin - resol - is formed by reaction in an alkaline environment even at a molar ratio of phenol to formaldehyde in the reaction mixture greater than 1. Even in this case, more than 1 mol of formaldehyde binds to 1 mol of phenol, i.e. ur203735 and remains in the reaction product. Because in a fully cured resol, if we assume the bond between the individual aromatic rings with methylated bridges, it could be. Theoretically, it is not economically desirable to prepare resols with an excessively high content of bound formaldehyde, since this is largely released during curing and lost to no avail. In contrast, technical reasons, such as the requirement to achieve low viscosity and high water solubility or the requirement for low free phenol content, higher reactivity, and the like, often necessitate the use of a higher molar excess of formaldehyde. Therefore, the specific conditions of preparation in individual cases usually represent a compromise between the two trends.

The chemical reaction yielding phenol-formaldehyde resole resins, i.e. polycondensation, is one of the sequential reactions with stable products, i.e. the reaction can be stopped at any stage, possibly only interrupted and then resumed. The polycondensation process requires external energy and is therefore carried out in practice by heating the reaction mixture. By lowering the temperature (cooling) of the reaction mixture, the reaction is slowed down or reduced. from a practical point of view. Thus, by selecting the temperature and reaction time, products of different average molecular weights, with different viscosities, can be obtained.

The mechanism of resol formation involves two basic types of reaction, namely the addition of formaldehyde to the phenol and, secondly, the condensation of the formed phenol-alcohols with each other or with the phenol to cleave the water. At lower reaction temperatures, more addition is promoted, at higher temperatures condensation. Thus, the temperature at which the reaction is conducted also has an influence on the qualitative course of the resin formation, i.e. the temperature of the reaction. the chemical structure and the resulting properties of the resin.

The patent literature discloses a number of different methods and processes for preparing phenol-formaldehyde resins aimed at achieving such product properties that are required for a particular application or to achieve a more economical production aspect. The patents relate in particular to various variations of the synthetic procedures (e.g., U.S. Pat. No. 1,089,970, .1,182,428,

240 274, 1 570 377 and 1 720 591, French. U.S. Pat. Nos. 1,416,472 and 2,057,858, Switzerland. U.S. Pat. No. 346 697 and 366 670), mainly reaction conditions (e.g. USSR No. 116 938, Germany No.

001103, US No. 3,485,797, French. U.S. Pat. No. 1,307,292), the sequence of added reaction components (U.S. Pat. No. 84,506, French Pat. No. 1221797, British Pat. No. 835,548, etc.), catalyst types, and combinations thereof (e.g., U.S. Pat. US Patent Nos. 170,655 and 171264, British Pat. No. 1,023,881, Australian Pat. No. 212,077, product purification and stabilization (e.g., USSR Pat.

No. 174,354, 193,056, Germany No. 1927,254, US No. 3,546,153, French. U.S. Pat. No. 2 043 775), intensification of production (eg French Pat. No. 1 412 255, 2 074 054, German Pat. No. 2 063 245) etc.

However, there is an interdependence between the various parameters of the preparation of phenol-formaldehyde resins affecting the properties of the resins, so that their variability in terms of the achievement of the desired complex of property values is limited. Therefore, in many cases, the desired properties can only be achieved by retrofitting a previously prepared resin product, such as removing unreacted components or catalysts, e.g. U.S. Pat. No. 96,929), increasing the reactivity by adding curing accelerators (U.S. Pat. No. 108,714, U.S. Pat. No. 3,186,960), adjusting the viscosity by adding suitable substances, and the like.

These technical and economic drawbacks of the prior art processes for the preparation of aqueous solutions of phenol-formaldehyde resols are solved by the present invention. The object of the invention is a process for the preparation of aqueous solutions of resol type phenol-formaldehyde resins, particularly suitable for impregnating cellulosic materials, in particular for laminates and molding films. The preparation is carried out by reacting 1 mole of phenol with 1 to 2.8 mole of formaldehyde in the presence of an alkaline catalyst at a temperature of 90 to 110 ° C, preferably at the boiling point of the reaction mixture for a time necessary to achieve the desired viscosity of the reaction product. resin concentration and / or addition to 10 wt. %, based on the resin content, of substances modifying the physical properties of the solution. The essence of the present invention is that the aqueous formaldehyde solution is added to the mixture of phenol and catalyst heated to the reaction temperature gradually, preferably continuously, so that the molar ratio of phenol to formaldehyde in the reaction mixture is at each point of the reaction up to at least 80 wt. % of the amount of phenol used is greater than 1.1, preferably greater than 1.5. Phenol can be partially or completely replaced by individual phenol homologs or mixtures thereof, aqueous formaldehyde solution partly by formaldehyde polymers.

Higher efficiency of this process of preparation of water-soluble resols compared to hitherto! According to known methods, by conducting the reaction at a constant high molar excess of phenol in the reaction mixture, the reaction conditions are less favorable for the formation of polymetolfenol compounds. Therefore, in the resulting reaction product there is a molar ratio between. formaldehyde bonded in the form of methylene bridges and formaldehyde bonded in the form of dimethylene ether bridges and / or methylol groups greater than that of known and applied methods for preparing resols with a molar excess of formaldehyde dehydrate in the initial reaction mixture. This results in a lower content of free phenol in the reaction product and a lower viscosity based on a comparable molar ratio of the total reaction components employed and a comparable solids (resin) content. Such a resin product has a significantly better ability to penetrate into cellulosic materials such as paper, so that higher concentration, i.e., less water, solutions can be used to impregnate such materials compared to the resin products obtained in a conventional manner, which is a significant economic effect. An important feature of the resole resin technology of the newly proposed process is the low content of unreacted components, even of low molecular weight, water vapor volatiles in the reaction mixture at the end of the preparation process, so that the distillation water many days of storage, which also represents a significant economic benefit.

A further advantage of the proposed process is the possibility of safely conducting the reaction even on an industrial scale on large-volume reactors at an economically advantageous boiling point of the reaction mixture, due to the uniform distribution of reaction heat evolution during the resin preparation process.

The higher effect of the process according to the invention as compared to the method applied so far is evident from the examples showing the addition procedures of the reaction time at boiling point, min.

handles 5 - - -10 20 May 30 40 52 phenol content moles 4.0 · 1.06 0.83 0.58 0.46 0.40 0.37 formaldehyde content moles 7.0 2.16 1.57 0.90 0.57 0.40 0.33 instant -mol. X ratio phenol / formaldehyde 0.57 0.49 0.53 0.64 0.80 1.00 1.12 The resulting resin product has these properties:

Refractive index n _D / 20 ° C 1.5386 viscosity MPa. s / 20 ° C 2020 content of brominable substances % - 4.1 water content, wt. % 23.1 gelatin, time at 150 ° C. per plate, with 82

Example 2

Into a three-necked 1500 ml flask equipped with a thermometer, stirrer, reflux and distillation condenser

376 g of phenol

161 g formalin (37.2%)

Sodium hydroxide solution (7.5 g) was added and the reaction mixture was introduced over 10 miB with the proper and appropriate product properties under comparable basic conditions of preparation. Example 1 relates to a conventional process for preparing aqueous solutions of phenol omaldehyde resol with a molar excess of formaldehyde in the feed, Example 2 to the process of the invention with a constant large molar excess of phenol in the reaction mixture. He did

In a three-necked 1500 ml three-necked sulfuric flask equipped with a thermometer, stirrer, reflux and distillation condenser:

376 g of phenol

565 g formalin (37.2%)

7.5 g of sodium hydroxide solution are added and the reaction mixture is brought to reflux at 20 DEG C. over a period of 20 minutes while maintaining a reflux condenser for 52 minutes when the reaction product condensation stage is reached, corresponding to the miscibility of the reaction product mixture with methanol. at a weight ratio of 1: 5 with water at a volume ratio of 1:13. The reaction product is cooled and subjected to distillation under reduced pressure to 9,06.10 ^-2 MPa 280 g distilled destilátu-. For the reaction mixture samples taken at 5 to 10 minute intervals during the reaction at the boiling point of the reaction. -the composition of the mixture was analyzed analytically at individual moments of the reaction:

at the boiling point. Once this temperature is reached, formalin is added dropwise to the reaction mixture at a constant rate such that 401 g of formalin is added dropwise over 50 minutes. After a further 13 minutes, the condensation step of the reaction product, corresponding to the miscibility of the mixture of the reaction product with methanol in a weight ratio of 1: 5 with water in a volume ratio of 1:13, is achieved. The reaction product was cooled and distilled under reduced pressure to 9,06.10 ^-2 MPa distilled 280 g of distillate.

Samples of the reaction mixture taken at 5- to 10-minute intervals during the reaction at the boiling point of the reaction mixture were analyzed analytically for their composition at each point in the reaction of the batch composition 5 phenol mol content 4.0 2.5 formaldehyde mol content 2.0.0 35 instant mole. phenol / formaldehyde ratio 2.0 7.2

The resulting resin product refractive index n _D / 20 ° G viscosity mPa. s / 20 ° C content of brominable substances, mass,%.

reaction time at boiling point, min

10 20 May 30. .40 50 ⁸³ 1,8 0.96 0.61 0.45 0.34 0.2: 5 0.53 0.52 0.46 0.42. ^; 0.40 0.30 4.5 2.4 1.53 of 1.12 0.85 0.83

these Properties: 1.5380 formaldehyde content, wt. % 0.7 1350 water content, mass % 23.0 81 3.4 gelatin, time at 150 ° C, on board, p

Claims (3)

SUBJECT A process for the preparation of aqueous solutions of resol type phenol-formaldehyde resins, particularly suitable for impregnating cellulosic materials, in particular for laminates and compression films, by reacting 1 mole of phenol with 1 already 2.8 mole of formaldehyde in the presence of an alkaline catalyst at 90 to 110 ° C. preferably at the boiling point of the reaction mixture, for the time required to achieve the desired viscosity of the reaction product and optionally subsequent dewatering of the solution to the desired resin concentration and / or addition to 10 wt. %, based on the resin content, of the physical properties of the solution, characterized in that the aqueous formaldehyde solution is added to the solution of the phenol with the catalyst heated to. the reaction temperature, gradually, preferably continuously, so that the molar ratio of phenol to formaldehyde in the reaction mixture is at least 80 wt. % of the amount of phenol used is greater than 1.1, preferably greater than 1.5. 2. Process according to claim 1, characterized in that the aqueous formaldehyde solution is optionally partially replaced by formaldehyde polymers. 3. The process according to claim 1, wherein the phenol is optionally partially or completely replaced by individual phenol homologues or mixtures thereof.