CA1054293A - Thermosetting phenol-formaldehyde resins - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
Thermosetting pheno-formaldehyde resins having novel structures and properties are described. The resins are formed at a mole ratio of formaldehyde to phenol of above 1.7:1 in an aqueous reaction medium. The resins form acid-catalyzed, room-temperature stable and mobile resins which may be applied as is onto substrates for the formation of molded articles, such as rice husk boards.

Description

1~)54'~93 This inv~ntion relates to novel thermosetting phenol-formaldehyde resins and to their preparation.
In our Canadian Patent No. 1,015,889 there is described the production of certain novel thermosetting phenol-formaldehyde resins having a characteristic infra-red spectrum and containing benzyl ether linkages ortho to the phenolic hydroxyl group.
It has now been found that resins formed from mole ratios of formaldehyde to phenol of above about 1.7:1 have unique properties and characteristic infra-red spectra not exhibited by resins formed from mole ratios of formaldehyde to phenol of less than about 1.7:1.
Thus, while the resins all have high absorbance at a wave number of 1230 cm 1, the resins formed from a greater than 1.7:1 mole ratio exhibit a strong absorption at a wave number of 1030 cm l, a peak which is absent from the spectra of resins formed from less than 1.7:l mole ratios.
. Further, the ratio of absorbance at a wave number of 1030 cm 1, measured from a base line drawn between wave numbers of a wave number of 1130 cm 1 and a wave number of 9S0 cm l, to that at a wave number of 1230 cm , measured from a base line between wave numbers of 1130 cm 1, and 1310 cm l is greater than 0.67 in the spectra of the no.vel resins.
The novel resins of this invention exhibit properties - which lead to novel, unexpected and advantageous uses for resins formed from mole ratios of formaldehyde to phenol greater than about 1.7:1.
These novel properties arise from the differences in structure of the resins produced at the different mole ratios.
Thus, for a given solids loading, catalyst level based on phenol and reflux time, the resin viscosity decreases as the formaldehyde to phenol mole ratio increases and the resins cure rapidly at 1~54293 high temperatures of about 200C. However, the stability of the resins, after addition of acid catalyst, at room or near ambient temperatures of about 20 to 25C increases with in-creasing formaldehyde - 2a -, . ,~.. , to phenol mole ratios. ~S4 In typical end uses of resole-type phenol ~ formaldehyde resins, it is common practice to accelerate the rate of cure or thermosetting of the resins by the addition of small quantities of acid catalysts, such as, benzene sulfonic acid and para-toluene sulfonic acid.
Non-caustic resole-type phenol-formaldehyde resins that have an infra-red spectrum exhibiting high absorption at wave numbers of 1010, 1060 and 1230 cm are used for certain 1~ applications, such as rice husk board manufacture, and have a high viscosity at room temperature. These resins require heating to lower their viscosity before application to a substrate. Since such resins cure rapidly in the presence of acid at the elevated temperatures required for application to the substrate, resin and acid have to be applied separately to the substrate. (For example, see our U.S. Patent No. 3,850,677).
This mode of application is haphazard at best since proper contact of acid and resin on the substrate surface is by no means assured, and this has lead to ~he use of greater quan-tities of acid than otherwise would be required, resulting inuneconomic chemical use and often impaired product appearance.
However, at mole ratios of formaldehyde to phenol above 1.7:1, the viscosity of the resin is such as to allow near room tem-perature application and, after acid addition, for example, up-to about 2 to 3% of para-toluene sulfonLc acid, the resin exhibits stability which allows long storage before use and the application of the resin to the substrate in an acid cataly~ed form, thereby avoiding the necessity to apply catalyst separately.

105~293 Since a single-component, acid-catalyzed, room temperature-stable and rapidly-curable resin may be provided in accordance with this embodiment of the invention for application t~ the substrate in end uses of the resin, the quantity of acid catalyst required for adequate curing of the resin is considerably decreased, typically to about l/6th to l/lOth of that required when the resin and catalyst are applied separately, as required in the prior art, thereby leading to more economic utilization of materials and a vastly improved product appearance, especially in rice husk board production.
- Additionally, resins prepared using mole ratios of formaldehyde to phenol of greater than 1.7:1 require a viscosity of about 1000cps or more at 75 F to perform as satisfactory adhesives for rice husk boards.
One embodiment of the present invention, therefore, provides a room temperature-stable, acid-catalyzed and mobile thermosetting phenol-formaldehyde resin capable of rapid cure at elevated temperature, formed by reaction of formaldehyde and phenol in an aqueous reaction medium at a mole ratio of formal-dehyde to phenol of greater than about 1.7:1 and having a viscosityof from about 1000 to about 40,000 cps at about 75F.
The resins formed from a mole ratio of formaldehyde to phenol greater than about 1.7:1 may be used in a variety of useful adhesive applications. For example, the resins may be used in various spray applications, such as rice husk board and particle board production. The resins also may be used in paper lamination, foundry core applications and plywood production.

In cold set foundry applications for making core mould~, phenolic resins are commonly used. The resins used, however, are not the conventional resole-type resins but are generally modified with expensive and scarcely-available chemicals, such as furfuryl ~054Z93 alcohol and silanes. It was surprising to find that the resins of the present invention, while being very stable in the presence of small quantities of acid-catalysts, at room temperature, react rather rapidly at acid levels of about 20 percent or more and are quite suitable for cold set, room temperature cure type appli-cations.
A further surprising property is-the ability of these resins to cure under the influence of radio frequency. Radio frequency, for example, is commonly used where faster production cycles are required. Typical examples are scarf and end joining and preheating of mats in panel board manufacture. The con-ventional caustic-containing phenolic resins, however, are not suitable for these applications as they arc very heavily under the influence of the high frequency energy and tend to precure.
More sophisticated resins, such as the resorcinol-modified resins catalyzed with para formaldehyde are suitable for use under radio frequency. Such resins are not only prohibitively expensive but have very poor pot life.
However, when the resins of this invention, produced -20 from mole ratios of formaldehyde to phenol of at least 1.7:1 are used in plywood manufacture with radio frequency preheating, con-siderable benefits in production cycles are derived.
The resins of this invention preferably are formed by a one-step process in which phenol and formaldehyde are reacted, in quantities such that the mole ratio of formaldehyde to phenol exceeds about 1O7:1, in an aqueous reaction medium containing a metal carboxylate catalyst for the reaction, for example, zinc acetate, wholly at a temperature above about 90C, as described in more detail in copending Canadian Application Serial No.
225,026 filed concurrently herewith.
The resin formed by this procedure exhibits large .._ -1054'~g3 absorption at wave numbers of '230 cm 1, 1060 cm 1 and 1030 cm 1.
Upon addition of at least one strong acid to this resin, there results a decrease of at least 5% in the absorption at a wave - 5a -, ~".

054~3 number of 1060 cm and an increase of at least 5% in the absorption at a wave number of 1030 cm while leaving substan-tially unaffected the absorption at a wave number of 1230 cm 1 The latter thermosetting phenol-formaldehyde resin may be isolated.
The invention is illustrated by the following Examples.
In these Examples reference is made to the accompanying drawings, in which Figures 1 to 12 are infra-red spectra of a number of thermosetting phenol-formaldehyde resins.
Example 1 This example illustrates the formation of a phenol~
formaldehyde resin of the present invention.
Into a glass reaction vessel equipped with an agitator, a reflux condenser and a thermometer was charged 179~.1 g tl9.09 moles) of phenol, 2788.3 g (34.35 moles) of formaldehyde having a methanol content of less than 1.5 wt.% (corresponding to a formaldehyde to phenol mole ratio of 1.8:1), 144.8 g (0.034 moles and about 8 wt. ~ is based on phenol) of ~inc acetate dihydrate and 772.8 g of water, to provide a reaction mixture having a total reactants loading of 54.01%.
The mixture was heated rapidly to go + 2 C in 40+ 5 minutes. The temperature was raised further to reflux, tapproximately 100 C) over the next 15 minutes by controlling the rate of heating. The reaction mixture was kept under constant reflux for a total time of 210 minutes. About 105 minutes after commencement of the reflux began, a distinct phase separation was observed.
After the completion of the reflux period, the reaction mixture was cooled to 35 C and the agitation stopped. Cooling then was continued to about 25 C. The liquid resin phase was separated from aqueous phase. The resin was found to have a Brookfield viscosity of 2000 to 2300 cps at 120 F and a N.V.

solids content of 75 to 80 percent.

10542g3 Example 2 -This example illustrates the different structures obtained when resins are formed from different mole ratios o~
formaldehy~e to phenol.
A series of phenol-formaldehyde resins was prepared following the procedure of Example 1 using ~arying mole ratios of formaldehyde to phenol. An infra-red spectrum was taken for each resin.
To a sample of each resin was added 1% para ~oluene 1~ sulfonic acid (used as a 50% aqueous solution) and the infra-red spectrum again taken. The two sets of spectra appear as Figures 1 to 12, identified as follows:
Figure 1 Mole ratio 1.4:1 No acid Figure 2 Mole ratio 1.6:1 No acid Figure 3 Mole ratio 1.8:1 No acid ~igure 4 Mole ratio 2~0:1 No acid ' - Figure S Mole ratio 2.5:1 No acid Figure 6 Mole ratio 3.0:1 No acid ~igure 7 Mole ratio 1.4:1 Acid Added - 20 Figure 8 Mole ratio 1.6:1 Acid Added ; - Figure 9 Mole ratio 1.8:1 Acid Added Figure 10 Mole ratio 2.0:1 Acid Added Figure 11 Mole ratio 2.5:1 Acid Added Figure 12 Mole ratio 3.0:1 Acid Added - It will be seen from a comparison of the spectra of the resins both before and after acid addition that there is a clear strong absorption peak at a wave n~ber of 1030 cm 1 in the spectra of the 1.8 and above mole ratio resins whereas this peak is absent from the spectra of the 1.4 and 1.6 mole ratio resins.

1054Zg3 Fur~her, a comparison can be made between the ratios of absorption at a wave number of 1030 cm 1, measured from a base line drawn between ~ave numbers 1130 cm and 950 cm 1, to that at a wave number of 1230 cm 1, measured from a base line between wave numbers of 1130 cm and 1310 cm Analysis of the spectra of the 1.8:1 and above mole ratio materials reveals that prior to acid addition there is also a large absorption at a wave number o~ 1060 cm 1, and after-acid addition, there is a decrease in the absorption at a w~ve number of 1060 cm 1 and an increase in adsorption at a wave number of 1030 cm 1, In the case of the 1.6:1 and below mole ratio resins, the adsorption at a wave number of 1060 cm 1 increases.
.
The following Table I provides the appropriate comparisons:
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~059~Z93 I~ will be seen from the above Table I that the resins of mole ratio 1.8:1 and above not only have a distinct peak at a wave number of 1030 cm 1 but also a ratio of absorbance ~o that at a wave number of 1230 cm 1 greater than about 0.6, both before and after acid addition, whereas resins of mole ratio 1.6:1 and below not only do not exhibit such a peak at a wave number of 1030 cm 1 but also have a ratio of absorbance to that at a wave number of 1230 cm 1 less than 0.6, both before and after acid addition.
Example 3 This example illustrates the physical properties of phenol-formaldehyde resins formed at various mole ratios of phenol to formaldehyde.
A series of phenol-formaldehyde resins were prepared following the procedure of Example 1. Various properties of the resins were tested and the results are reproduced in the - following Table II:
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1054~93 The results of the above Table II indicate the decreasing viscosity of the resins at mole ratios of 1.8:1 and a~ove, the decreasing electrical resistance of the resins at mole ratios of 1.8:1 and above, the rapidly-decreasing cure times of acid catalyzed curings with increasing mole ratio and the ability to emulsify the resins at mole ratios of 1.5:1 and above.
The results of the above Table II also show that, contrary to the expectation of one practising this art, the electrical properties of the resins and the change in electrical properties of the resins after acid addition are independent of-the viscosity of the resin.
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' ,~ , ' , ' ~- , -. 12 1054X~3 ample 4 This example illustrates the ~ormation of rice husk - board from acid catalyzed resins.
A 75% solids resin formed by the procedure of Example 1 and having a mole ratio of formaldehyde to phenol o 1.6:1 was catalyzed with 0.5~ by weight of para-toluene sulfonic acid (used as a 50% solution) and was found to be stable at room temperature for o~er 24 hours. The resin, however, was incapable of being sprayed at room temperature due to its inherent viscosity ~50,000 cps at room temperature) and consequently had to be warmed to 160F for use. At this temperature, the resin gained - viscosity rapidly and hence could not be spray applied to the rice husks.
- The resin and acid catalyst, however, were capable of being satisfactorily applied to the rice husks as separate com-ponents. The acid first was sprayed onto samples of cleaned rice husks at levels of 4~ and 8% based on resin weight. There-after, ~he resin was hot meit sprayed at 150F onto the rice husk samples, in both cases at a resin solids leve~ of 10~ based ~0 - on husks. The resin coated husks were laid into mats, consolida-ted and then pressed in a hot press at 390F for a period of 11 - minutes.
An equivalent 75% solids resin formed by the procedure-of Example 1 and having a mole ratio of formaldehyde to phenol of 1.8:1, after catalyzing with 0.5% by weight of para-toluene sul-fonic acid (used as a 50% aqueous solution), was found to be stable at room temperature for prolonged periods of over a week.
The catalyzed resin was found to be sprayable at room tempera~ure and near ambient temperatures of 80 to 90F and rice husk boards were formed by spraying the cleaned husks with 10% of the acid catalyzed resin, followed by the mat formation, consolidation and hot pressing as outlined above. The resultant board of 1/2 inch _ 13 ~054293 thickness and 48 lb/ft3 density was very light in colour, in contrast to the typical rice husk boards formed from the two-component system which were quite dark in colour.
Similar rice husk boards were formed from one-component systems using resins at other mole ratios above 1.7:1.
The strength properties of the boards were determined and the results appear in the following Table III:
TABLE III
.
Type of Application Mole Ratio Catalyst Intemal Mbdulus of Level ~ Bond Rupture Strength psi psi Two-component 1.6:1 4 Dela~inated Two-component 1.6:1 8 75 1900 One-component 1.8:1 1 90 2100 One-component 2.0:1 108 One-component 2.5:1 76 One-component 3.0:1 55 One-component 3.0:1* 57 *-Deferred feed The results of the above Table III clearly -demonstrate that the abillty of a 1.8:1 mole ratio resin to be l~sed in a one-component spray application leads to the production of good quality rice husk boards with improved appearance and considerably lower catalyst levels than are required when a 1.6:1 mole ratio resin is applied in a two-component spraying procedure, the latter procedure being adopted due to the inability of the 1.6:1 mole ratio to be sprayed as a single component in a commercially-feasible manner.

~ - 14 -The results of the above Table III also demon-strate that good quality rice husk boards can be formed even from the very low viscosity resins provided at mole ratio of 3.0:1.
It has already been demonstrated in our U~S.
Patent No. 3,850,677 that resins of 1.6:1 mole ratio of low viscosity at room temperature are not suitable for the manufacture of rice - 14a -- lOS4293 ~nusk boards. The l~ter low viscosity resirs typically are prepared by the procedure-outlined in Canadian Patent No. 927,041 - at mole ratios of about 1.5:1.
Example 5 This example illustrates the use of various phenol-: formaldehyde resins in cold set foundry sand applications.
Sand was coated with 1.5~ by weight of resin andvarying amounts of catalyst levels by tumbling the mix in a tumbler. Cylindrical molding forms were made in a mold and allowed to ary under ambient temperature conditions. The forms were tested at various intervals for strength properties.

: .
: ~ The results are reproduced in the following Table IV; along with comparative data on commercially-available ~-~ - resins: .
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~ _ _ O s ~ 4 0 ~ U)~ ~ 0 -td ,,~ Z ~' The results of the above Table IV indicate the sui~-ability of the resins of mole ratio of 1.8:1 in cold foundry sand - applic~tion. These results are in contrast to experiments con-~ucted with resins formed at a mole ratio of 1.6:1 which showed that similar mouldin~ ~orms could not be made at the catalyst levels of 20~ or more outlined in Table IV. Considerable precure~
occurred and the resulting moulding forms lacked strength and integrity.
It will be seen therefore that the present invention provides novel resins which have superior adhesive properties in many applications. Modifications are possible within the scope of the invention.

;

Claims (11)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A room temperature-stable, acid-catalyzed and mobile thermosetting phenol-formaldehyde resin capable of rapid cure at elevated temperature, formed by reaction of formaldehyde and phenol in an aqueous reaction medium in the presence of a metal carboxylate therefor at a mole ratio of formaldehyde to phenol of greater than about 1.7:1 and acid catalysis of the resin so formed, and having a viscosity of about 1000 to 40,000 cps at 75°F.

2. The resin of Claim 1 wherein said mole ratio is from about 1.8:1 to about 3.0:1.

3. A method for the production of a room temperature-stable, mobile thermosetting phenol-formaldehyde resin capable of rapid cure at elevated temperature which comprises:
reacting phenol and formaldehyde together in a mole ratio of formaldehyde to phenol greater than about 1.7 to 1 in an aqueous medium in the presence of a water-soluble metal carboxylate catalyst therefor to form a thermosetting phenol-formaldehyde resin having benzyl ether linkages ortho to the phenolic hydroxyl group and an infra-red spectrum which dis-plays large absorption at wave numbers of 1230 cm-1 , 1060 cm-1 and 1030 cm-1, reacting said resin with at least one strong acid to cause a decrease of at least 5% in said absorption at wave number of 1060 cm-1 and an increase of at least 5% in said absorption at wave number of 1030 cm-1 while leaving substantial-ly unaffected said absorption at wave number of 1230 cm-1, and isolating the phenol-formaldehyde resin so formed.

4. The method of Claim 3 wherein said phenol and formaldehyde are reacted together in a single step carried out wholly at a temperature above about 90°C.

5. The method of Claim 3 wherein said strong acid is para-toluene sulfonic acid.

6. A composition comprising a free flowing mass of sub-divided material consisting of individual elements having a coating over at least part of the surface thereof of a room temperature-stable, acid-catalyzed and mobile thermosetting phenol-formaldehyde resin capable of rapid cure at elevated temperature, formed by reaction of formaldehyde and phenol in an aqueous reaction medium in the presence of a metal carboxylate catalyst therefor at a mole ratio of formaldehyde to phenol of greater than about 1.7:1 and acid catalysis of the same, and having a Viscosity of about 1000 to 40,000 cps at 75°F.

7. The composition of Claim 6 wherein said individual elements are grains of foundry sand.

8. The composition of Claim 6 wherein said individual elements are rice husks.

9. The composition of Claim 6 wherein said individual elements are wood chips.

10. The composition of Claim 6 wherein said individual elements are wheat straw.

11. The composition of Claim 6 wherein said individual elements are rye grass.