GB2079298A - Quick-curing phenolic resin - Google Patents

Abstract

A process for producing a quick- curing phenolic novolac resin having an ortho linkage/para linkage ratio of 0.9-3.0 and a number average molecular weight of the resin exclusive of free phenol of 600-1,100, comprises reacting one mole of a phenol with 0.6-0.95 mole of formaldehyde at a temperature of more than 100 DEG C with a combination of (A) a catalyst effective for the addition reaction selected from divalent metal salts with (B) a catalyst effective for the condensation reaction selected from divalent metal salts, said catalysts (A) and (B) being used from the start of the reaction, or comprises reacting both the reactants under reflux in the presence of said catalyst (A), then adding an acid to adjust the pH value of 1-5, immediately thereafter removing water under reduced pressure and further reacting the product under normal pressure at a temperature of more than 100 DEG C. Suitable acids are hydrochloric or salicylic acid. The catalysts (A) and (B) are preferably salts of alkaline earth metals or transition metals with either an organic monocarboxylic acid (catalyst A) or an inorganic acid (catalyst B).

Description

SPECIFICATION Quick-curing phenolic resin, a process for its manufacture, and shaped structures derived therefrom This invention relates to an industrial process for producing quick-curing phenolic resins. The characteristic feature of this invention consists in producing a high-ortho phenolic resin safely, easily and at low cost by use of an appropriate combination of a diva lent metal salt effective for the addition reaction and a diva lent metal salt or an acid effective for the condensation reaction.

Since H. L. Bender et al. reported that a high-ortho phenolic novolac resin having a high ortho linkage content has a quick-curing property, a variety of production processes have been proposed for this high-ortho phenolic novolac resin.

High-ortho phenolic novolac resins are usually produced by first producing a methylol-phenol form with a weakly acidic diva lent metal salt as a catalyst, followed by condensing the same. In this case, if the reaction is carried out with only one kind of weakly acidic divalent metal catalyst, it is difficult to keep a good balance between the reaction veiocities of addition reaction (methylolation) and condensation reaction (methylene formation) during the progress of the reactions, so that there arise problems such that the reaction system forms a gel, that a phenolic resin having only a small ortho/para linkage ratio is produced, and the like.

The present inventors have studied the reaction in detail and have discovered the role played by the divalent metal salt and the reaction mechanism in the production of a high-ortho phenolic resin, and as a result of their discoveries have invented an industrial production process which results in a highortho phenolic resin.The inventors have appreciated from their studies that the formation of a phenolic resin having a high ortho/para linkage ratio (hereinafter referred to as o/p ratio) using a diva lent metal salt is only made possible by forming the ortho-methylol product by a reflux reaction and then condensing the ortho-methylol product at a temperature of more than 1 000C, at which the paraselectivity of the reaction is weakened, whereas, if the condensation is carried out at a tempeature of not more than 1000 C, the condensation proceeds preferentially at the para-position even in the presence of a divalent metal salt, so that only a phenolic resin having a small o/p ratio is obtained.

Further, it has also been found that the dissociation constant and solubility of the divalent metal salt determines the selectivity of the addition-condensation reaction, namely that a divalent metal salt having a low dissociation constant and a low solubility is effective for the addition reaction (methylolation), while a divalent metal salt having a high dissociation constant and a high solubility is effective for the condensation reaction (methylene formation).

The present inventors have found that when catalysts different in action are used in an appropriate combination and the condensation reaction is carried out at a temperature of more than 1 000C, both addition reaction and condensation reaction proceed with a good balance, whereby a high-ortho type of quick-curing phenolic resin can be produced safely, easily and inexpensively.

According to this invention, there is provided a process for producing a quick-curing phenolic resin having an o/p ratio of 0.9-3.0 and a number average molecular weight of the resin exclusive of free phenol of 600-1,100, which comprises reacting a phenol (P) and formaldehyde (F) in a F/P molar ratio of 0.6-0.95 at a temperature of more than 1 000C with a combination of (A) a catalyst effective for the addition reaction selected from diva lent metal salts and (B) a catalyst effective for the condensation reaction selected from divalent metal salts, said combination being used from the start of the reaction, or comprises subjecting said phenol and formaldehyde to a reaction under reflux in the presence of the (A) catalyst only to form an ortho-methylol-phenol product, adding an acid to the system until the pH becomes 1-5 which is a value effective for the condensation reaction, immediately thereafter removing water under reduced pressure, and then subjecting the product to a further reaction at normal pressure at a temperature of more than 1 000C. It is particularly effective to use one or more salts of alkaline earth metals or transition metals with organic monocarboxylic acids as the (A) catalyst and one or more salts of alkaline earth metals or transition metals with inorganic acids as the (B) catalyst. The term "transition metals" used herein means metals selected from the first and second transition elements having an atomic numbers of 21-30 and 39-48 in the Periodic Table.As said acid, it is effective to select one or more acids having an optimum solubility and dissociation constant for obtaining the desired pH value. When a pH value of, for example, about 4 is desired, it is preferable to use not a slight quantity of hydrochloric acid but a large amount of salicylic acid.

The molar ratio of the catalyst (A) to the catalyst (B), when used in combination, is advantageously 0.02-4. When it is less than 0.02, the yield is extremely low. When it is more than 4, there is a danger of gelation. The amount of the divalent metal salt used is advantageously 0.13% by weight based on the weight of phenol charged. That is, when the catalysts (A) and (B) are used in combination the total amount of both catalysts is 0.13% by weight based on the weight of phenol charged, while when the catalyst (A) and an acid are used in combination the amount of the catalyst (A) is 0.13% by weight based on the weight of phenol charged. When the amount of the divalent metal salt is less than 0.1% by weight, the yield is extremely low.When it is more than 3% by weight, the salt content in the phenolic resin becomes not negligible and may adversely affect the electrical properties.

When the catalyst (A) and an acid are used in combinatitn, it is desired that the consumption of formaldehyde is 5095% by weight and the consumption of the phenol is 3075% by weight, at the time of completing the reflux. If the consumptions are too small, a low molecular weight resol is mainly formed, so that the subsequent reaction is difficult to control and there is a fear of gelation. If the consumptions are too great, the condensation reaction progresses excessively, and the phenolic resin obtained has a relatively low o/p ratio.

When the catalyst (A) and an acid are used in combination, it is desired that the dehydration under reduced pressure after addition of the acid is effected until the water content of the reaction system becomes 5% by weight or less. In the step of dehydration under reduced pressure after addition of acid, it is desirable to make the water content of the system not more than 5% by weight in order to suppress the generation of heat due to addition of acid, to make the reaction system approach a non-aqueous state, to accelerate the subsequent condensation reaction and to facilitate the temperature control in the condensation reaction. When it is more than 5% by weight, the condensation temperature is kept in a low level owing to the heat of vaporization of water, so that only a phenolic resin having a low o/p ratio is obtained.

As the formaldehyde source, it is preferable to use paraformdldehyde having a low water content when the catalysts (A) and (B) are used in combination and to use formalin having a high water content when the catalyst (A) and the acid are used in combination. When the catalysts (A) and (B) are used in combination, the low water content, namely, the use of paraformaldehyde, is preferable for securing a temperature of more than 1 000C at normal pressure. On the other hand, super-atmospheric pressure is required to secure a temperature of more than 1000C when formalin is used.When the catalyst (A) and the acid are used in combination, the use of formalin having a high water content is preferable for controlling the addition reaction, absorbing the heat generated at the time of adding the acid and dispersing the reaction system uniformly. When paraformaldehyde is used in said case, the reaction is difficult to control.

The phenolic resin obtained according to this invention has an o/p ratio of 0.9-3.0 and a number average molecular weight of the resin exclusive of free phenol of 600-1,100. The desired o/p ratio can be obtained by varying the ratio of the catalyst (A) to the catalyst (B) or by adjusting the pH value after addition of acid, and the desired molecular weight can be obtained by varying the F/P at the time of charge. That is, by this invention, resins having an o/p ratio and a molecular weight falling in the abovementioned ranges can freely be obtained safely, easily and inexpensively.

From the phenolic resin obtained by this invention, there can be obtained molding materials having various curability and flowability. Particularly, a molding material formed from a phenolic resin having an o/p ratio of 1.0-1.5 and a number average molecular weight of the resin exclusive of free phenol of 700--900 exhibits the features that it has a good heat-stability, a good flowability and a quick-curing property and enables the shortening the molding time in a large scale molding, whereby high cycle molding is made possible. Further, owing to its excellent flowability and melting property, addition of plasticizer becomes unnecessary, so that problems such as dulling of mold, bad appearance of molded product and the like can be eliminated.

This invention is explained below referring to Examples and Comparative Examples. The Examples are by way of illustration and not by way of limitation.

In the following Examples and Comparative Examples, the curability, the o/p ratio, the number average molecular weight and the Barcol hardness were determined in the following manner.

1) Curability Instrument used: Curelastometer as disclosed in U.S. Patent No. 3,479,858 and British Patent No. 1,126,995.

Measuring Conditions Die temperature: 1 500C Molding pressure: 100 kg/cm2 Angle of oscillation: 0.50 2) o/p ratio The amount of the protons of ortho-methylol, para-methylol, ortho-ortho bonded methylene, ortho-para bonded methylene and para-para bonded methylene was measured by means of a nuclear magnetic resonance spectrometry (NMR), from which the ortho linkage/para linkage ratio was calculated from the following equation::

1/2 ortho orthoortho 1 /2 ortho methylol \ linkage p ara linkage methylene } + methylene + methylene protons / protons ,protons o/p ratio = 1/2 para- \ lpara-para 1/2 ortho methylol \ + linkage + para linkage methylene i methylene \ methylene protons / protons \ protons 3) Number average molecular weight It was measured by a vapor pressure equilibrium method. The number average molecular weight of the resin exclusive of free phenols was calculated from the measured value of number average molecular weight and the amount of free phenols determined by gas chromatography.

4) Barcol hardness Apparatus: Barcol Impresser 935 Curing conditions: 1 750C, 20 seconds Time of measurement: 10 seconds after taking the sample out of the mold.

EXAMPLE 1 282 g of phenol and 87 g of 88% by weight paraformaldehyde (F/P = 0.85) were subjected to reaction under reflux for 3 hours in the presence of 1.96 g of zinc chloride and 0.11 g of barium acetate.

(The temperature inside the reaction vessel varied from 11 50C to 1 050C.) Subsequently, the reaction mixture was dehydrated by heating at normal pressure and taken out into a vat when the internal temperature had reached 1 500C. 285 g of a resin having an o/p ratio of 1.1, a number average molecular weight of the resin exclusive of free phenol of 805 and a free phenol content of 7.0% by weight was obtained.To 100 parts by weight of this resin was added 1 5 parts by weight of hexamethylenetetramine, and the gel time was measured on a hot plate kept at 1 500C (hereinafter, this gel time is referred to as "hot plate gel time"), and found to be 43 seconds. Further, 1 8 parts by weight of hexamethylenetetramine, 65 parts by weight of woodflour, 25 parts by weight of calcium carbonate and 3 parts by weight of stearic acid were added to 100 parts by weight of this resin and the mixture was kneaded on hot rolls at 1000C for 5 minutes to obtain a molding material. This material was formed into a molded article, which had a Barcol hardness of 52. When a high-para novolac phenol resin produced with a usual acid catalyst (Comparative Example 4) was used, the Barcol hardness was as low as 25 for the same formulation.

EXAMPLE 2 282 g of phenol and 1 60 g of 45% by weight formalin (F/P = 0.80) were subjected to reaction under reflux for 3 hours in the presence of 3.0 g of manganese acetate (the consumption of phenol was 40% by weight and the consumption of formaldehyde was 81% by weight). Then, 0.1 g of 30% by weight hydrochloric acid was added (pH 1.1), after which the mixture was dehydrated under reduced pressure for 30 minutes (water content 1%). Thereafter, the temperature was stepwise raised from 1 050C to 1 500C in 3 hours to obtain 285 g of a resin having a free phenol content of 6.0% by weight, an o/p ratio of 1.1 and a number average molecular weight of the resin exclusive of free phenol of 750.

This resin had a hot plate gel time of 51 seconds. In the case of the usual high-para novolac phenol resin, the gel time is about 91 seconds. Further, the curability, i.e. maximum degree of cure and curing rate, of the same sample as used in the measurement of gel time was measured by means of Curelastometer (a trade name of Japan Synthetic Rubber). The results were as shown in Table 1. The resin obtained in the present Example is superior to high-para novoiac phenol resin (Comparative Example 4) in both maximum degree of cure and curing rate, demonstrating its quick-curing property.

COMPARATIVE EXAMPLE 1 In the same manner as in Example 2,282 g of phenol and 195 g of 37% by weight formalin (F/P = 0.80) were subjected to reaction in the presence of 2.8 g of zinc chloride without adding hydrochloric acid and then taken out onto a vat. Thus, 240 g of a resin having a free phenol content of 6.2% by weight, an o/p ratio of 0.9, a number average molecular weight of the resin exclusive of free phenol of 650 and a hot plate gel time of 63 seconds was obtained. As compared with the products of Example 1 and Example 2, this resin was lower in not only o/p ratio and molecular weight but also yield.

EXAMPLE 3 A mixture of 282 g of phenol and 81.8 g of 88% by weight paraformaldehyde (F/P = 0.80) was slowly heated from room temperature to 1000C in 30 minutes and then from 1000C to 1 500C in one hour in the presence of 1.6 g of zinc chloride and 0.66 g of zinc acetate. Thereafter, the mixture was kept at a reduced pressure of 80 mm Hg and then taken out onto a vat. Thus, 289 g of a resin having a free phenol content of 7.6% by weight, an o/p ratio of 1.5, a number average molecular weight of the resin exclusive of free phenol of 850 and a hot plate gel time of 37 seconds was obtained. As measured with Curelastometer, the curability of the resin was as shown in Table 1.Further, a molding material was prepared therefrom in the same manner as in Example 1, and the Barcol hardness of a molded article of the molding material was measured to be found 57.

EXAMPLE 4 282 g of phenol and 187 g of 37% by weight formalin (F/P = 0.77) were subjected to reaction under reflux for 3 hours in the presence of 3.3 g of zinc acetate (consumption of phenol, 60% by weight; consumption of formaldehyde, 90% by weight), after which 4.1 g of salicylic acid was added thereto (pH 3.5). After dehydration under reduced pressure (water content, 2% by weight), the mixture was slowly heated from 1000C to 1 500C in 3 hours, to obtain 288 g of a resin having a free phenol content of 5.8% by weight, an o/p ratio of 1.8, a number average molecular weight of the resin exclusive of free phenol of 800 and a hot plate gel time of 28 seconds.As measured with Curelastometer, the curability of the resin was as shown in Table 1. A molding material was prepared therefrom in the same manner as in Example 1 and formed into a molded article. The insulation resistance of the molded article was 3.1 x 1010 Q in the normal state and 5.7 x 109 Q after being boiled.

COMPARATIVE EXAMPLE 2 282 g of phenol and 190 g of 37% by weight formalin were subjected to reaction under reflux for 2 hours in the presence of 1.6 g of zinc acetate (consumption of phenol, 50% by weight; o/p ratio, 2.5).

The mixture was heated for an additional 2 hours (consumption of phenol, 80% by weight; o/p ratio, 1.6). Then, 1.5 g of oxalic acid was added (pH 2.1), and the resulting mixture was heated under reflux for 2 hours. Thereafter, the mixture was dehydrated and concentrated under normal pressure and then heated to 1 500C in 3.5 hours, to obtain 285 g of a resin having a free phenol content of 7.0% by weight, an o/p ratio of 0.9, a number average molecular weight of the resin exclusive of free phenol of 820 and a hot plate gel time of 51 seconds.These results demonstrate that the o/p ratio drops when the reaction is effected at a temperature of not more than 1000C even in the presence of a divalent metal salt and that the o/p ratio drops when the temperature of condensation is not more than 1000C.

As compared with the resin of Example 3 and Example 4, this resin was lower in o/p ratio and inferior in quick-curing property. Moreover, it necessitated a reaction time of more than 2 hours longer than that in Example 1, Example 2, Example 3 and Example 4.

EXAMPLE 5 In the same manner as in Example 1, 286 g of a resin was prepared by reacting 282 g of phenol and 79 g of 88% by weight paraformaldehyde (F/P = 0.77) in the presence of 0.8 g of manganese nitrate and 1.9 g of zinc acetate. This resin had a free phenol content of 6.0% by weight, an o/p ratio of 2.0, a number average molecular weight of the resin exclusive of free phenol of 900 and a hot plate gel time of 23 seconds. A molding material was prepared therefrom in the same manner as in Example 1, and formed into a molded article. It had a Barcol hardness of 60.

EXAMPLE 6 282 g of phenol and 195 g of 37% by weight formalin (F/P = 0.80) were subjected to reaction under reflux for 3.5 hours in the presence of 1.5 g of manganese acetate (consumption of phenol, 50% by weight; consumption of formaldehyde, 93% by weight). After adding 1.0 g of benzoic acid (pH 5.0), the mixture was immediately concentrated under reduced pressure (water content, 3% by weight).

Then, the mixture was stepwise heated to 1 500C in 3 hours, to obtain 292 g of a resin having a free phenol content of 8.0% by weight, an o/p ratio of 2.5 and a number average molecular weight of the resin exclusive of free phenol of 900. As measured with Curelastometer, the curability of this resin was as shown in Table 1.

COMPARATIVE EXAMPLE 3 282 g of phenol and 1 60 g of 45% by weight formalin were subjected to reaction under reflux for 3 hours in the presence of 3.0 g of manganese acetate and 0.1 g of 30% by weight hydrochloric acid.

Then, the mixture was subjected to dehydration in the same manner as in Example 2, and taken out onto a vat. The resin thus obtained was a high-para phenol novolac resin. Although in the present Example the F/P, the catalysts, and the amount of catalysts were the same as in Example 2, no highortho resin was obtained because the divalent metal salt was added at once at the start of the reaction.

COMPARATIVE EXAMPLE 4 282 g of phenol and 1 95 g of 37% by weight formalin were subjected to reaction under reflux for 3 hours in the presence of 3 g of oxalic acid, after which the mixture was dehydrated under normal pressure and heated to 1 5O0C in 4 hours. The resin thus obtained was a high-para phenol novolac resin having a free phenol content of 7% by weight, an o/p ratio of 0.75 and a number average molecular weight of the resin exclusive of free phenol of 850. The curability of this resin was measured with Curelastometer in the same manner as in Example 2. The results were as shown in Table 1, which demonstrate that the curing reaction of this resin is much slower than that of the resins obtained in the Examples.

COMPARATIVE EXAMPLE 5 In the same manner as in Example 2,282 g of phenol and 1 70 g of 37% by weight formalin (F/P = 0.70) were reacted in the presence of 3.3 g of zinc acetate without adding hydrochloric acid.

When the inner temperature reached 1 450C, a violent reaction took place and a gel was formed.

TABLE 1 Curability measured with Curelastometer

Comparative Example Example Example Example Example 2 3 4 6 4 Maximum 9.0 87 8.5 7.5 6.2 degree of cure (kg) Curing 3.8 5.2 5.8 8.1 2.1 rate (kglmin)

Claims (13)

1. A process for producing a quick-curing phenolic resin having an ortho linkage/para linkage ratio of 0.9-3.0 and a number average molecular weight of the resin exclusive of free phenol of 600-1,100, which comprises reacting one mole of a phenol with 0.6-0.95 mole of formaldehyde at a temperature of more than 1000C with a combination of (A) a catalyst effective for the addition reaction selected from divalent metal salts with (B) a catalyst effective for the condensation reaction selected from divalent metal salts, said catalysts (A) and (B) being used from the start of the reaction, or comprises reacting both the reactants under reflux in the presence of said catalyst (A), then adding an acid to adjust the pH value to 1-5, immediately thereafter removing water under reduced pressure and further reacting the product under normal pressure at a temperature of more than 1000C.

2. A process according to Claim 1, wherein the catalyst (A) is one or more salts of an organic carboxylic acid with an alkaline earth metal or a transition metal selected from the first and the second transition elements having atomic numbers of 21-30 and 39-48 in the Periodic Table.

3. A process according to Claim 1, wherein said catalyst (B) is one or more kind of salt of an inorganic acid with an alkaline earth metal or a transition metal selected from the first and the second transition elements having atomic numbers of 21-30 and 39-48 in the Periodic Table.

4. A process according to Claim 3, wherein the combination of the catalyst (A) with the catalyst (B) is used, the molar ratio of the catalyst (A) to the catalyst (B) is 0.02-4, and the total amount of the catalysts is 0.1-3% by weight based on the weight of the phenol charged.

5. A process according to Claim 3 or 4, wherein the combination of the catalyst (A) with the catalyst (B) is used and the formaldehyde is used in the form of paraformaldehyde.

6. A process according to Claim 1 or 2, wherein the combination of the catalyst (A) with the acid is used, and the amount of the catalyst (A) is 0.13% by weight based on the weight of the phenol charged.

7. A process according to Claim 6, wherein the consumption of formaldehyde is 5095% by weight and the consumption of phenol is 3075% by weight when the reflux is completed.

8. A process according to Claim 6, wherein the dehydration under reduced pressure after the addition of the acid is effected until the water content in the reaction system becomes not more than 5% by weight.

9. A process according to Claim 6,7 or 8, wherein the formaldehyde is used in the form of formalin.

1 0. A process as claimed in claim 1, carried out substantially as described in any one of Examples Nos. 1 to 6 herein.

11. A phenoiic resin whenever prepared by a process as claimed in any one of claims 1 to 10.

12. A shaped structure, comprising a resin as claimed in claim 11 that has been cured.

13. A shaped structure as claimed in claim 12, that is an electrical insulator.