AU1539100A - Phenol formaldehyde resins - Google Patents

Description

WO 00/31160 PCT/AU99/01054 PHENOL FORMALDEHYDE RESINS Field of the Invention The present invention relates to fast cure resins. 5 More particularly, the present invention relates to fast cure resins which are less expensive to produce. This invention also relates to a method of synthesising such fast cure resins, in which the processing time has been significantly reduced. 10 Background to the Invention Commercial phenol-formaldehyde resins, developed previously by the present inventors, included those which were a carbonate-catalysed low alkalinity Novalac precursor 15 and the addition to resins of very high HLB surfactants (approximately 30-40) to facilitate rapid water loss from the glueline favouring the condensation and curing reaction. Such technology is the subject of patent applications owned by the Commonwealth Scientific and Industrial Research 20 Organisation. These commercialised resins have been used for the gluing of slash and radiata pine plywood. Whilst both of these resin types offer somewhat better performance, especially for the gluing of Eucalypts, at approximately equivalent cost compared with other phenol-formaldehyde 25 resins, their cost advantage is somewhat eroded due to the addition of surfactants as cure promoters, as discussed above. The cost of the added surfactants is roughly 5.7 cents/kilogram for the resin incorporating hydrocarbon/fluorocarbon surfactants and roughly 2.0 30 cents/kilogram for the resin incorporating only the hydrocarbon surfactant. The present inventors therefore set about developing a new type of resin that offered greater performance and one which eliminated the requirement for the synergistic effect of surfactants, such that a significant 35 cost advantage might be realised. Conventional phenolic resins for use in manufacturing adhesives for wood-based products, such as WO 00/31160 PCT/AU99/01054 -2 plywood, laminated veneer lumber (LVL), particleboard (PB), medium-density fibreboard (MDF) and similar wood-based products, are known as resoles. Resoles are usually prepared by reacting phenol with formaldehyde in the 5 presence of a strongly alkaline agent such as sodium or potassium hydroxide. The initial reaction, known as methylolation, which is promoted by strong alkali, is often carried out in the presence of approximately 25-40% of the final alkali content. The molar ratio of formaldehyde to 10 phenol is typically about 1.5 to about 3.5 and the reaction is highly exothermic in its initial stages and very difficult to control so that the provision of adequate cooling is essential to maintain control of the reaction temperature. Once the initial output of heat has subsided, 15 the reaction temperature may be safely increased to promote resin condensation. The reaction between phenol and formaldehyde proceeds via the linking of phenolic rings through bridging methylene groups. Such a reaction usually proceeds by acid 20 or base catalysis. If base catalysed, the phenol is converted into the phenoxide ion making it far more reactive (nucleophilic), facilitating the electrophilic substitution on the ring by the electron deficient carbon of formaldehyde. If acid catalysed, the oxygen atom of the 25 formaldehyde group becomes protonated, thereby increasing the electron deficiency of the carbonyl carbon, facilitating the nucleophilic addition of the aromatic ring to the carbonyl group. The methylol groups, thus formed, react further resulting in the formation of polymers, having 30 increasing molecular weights. As the reaction proceeds, the viscosity of the reaction mixture naturally increases due to the formation of phenol-formaldehyde polymers, whose molecular weight increases as the reaction progresses. This increase in 35 viscosity must be carefully monitored and is frequently used to determined when further additions of agent should be made to increase the solubility of the resin as well as to reduce WO 00/31160 PCT/AU99/01054 -3 its viscosity. If the viscosity is increased too much, cross-linking between polymers and eventually gelation results. This must be avoided if the resulting resin is to be used in the manufacture of wood adhesives. 5 Required levels of alkalinity and resultant pH need to be achieved, as they are necessary to solubilise polymers of sufficient molecular weight for adhesives for reconstituted wood products. Typical phenol-formaldehyde resins for adhesive applications for wood-based adhesives 10 such as plywood and LVL consist of 41-44% of resin solids, 6-8% alkalinity and have a pH of 12.5-13.5. In a previous attempt to reduce the solubilising effect of highly alkaline resins (pH 12.5-13.5) on the extractives of blackbutt, Eucalyptus pilularis, by the 15 addition of acids and acid salts, it was found that the cure speed of the resin increased markedly as the pH was reduced. Unfortunately, at the same time, the viscosity of the resin also increased enormously making it completely useless as an adhesive for plywood. However, these results indicated that 20 the reaction rate was greatly increased at approximately pH 11.0. Whilst phenolic resins can be synthesised at pH 11.0, they are not suitable for such applications as plywood and LVL because of their very low molecular weight (low condensation), as higher molecular weight components cannot 25 be solubilised without the addition of strong alkali and subsequent increase in pH. In this specification, the term "phenol" can be extended to include any aromatic hydroxy derivative. The present invention therefore seeks to provide a 30 process for the synthesis of a fast cure phenol-formaldehyde resin, wherein the reduction in cure speed effect of highly alkaline resins is reduced and one in which the required viscosity is achieved. The present invention also seeks to provide a fast cure phenol-formaldehyde resin that offers 35 greater adhesive performance and eliminates the need for the synergistic effect of surfactants, thus affording a significant cost advantage to the manufacture of such a WO 00/31160 PCT/AU99/01054 4 resin for use in the manufacture of wood adhesives. Summary of the Invention According to the present invention, there is 5 provided a process for the synthesis of a phenol formaldehyde resin including an initial step of forming a phenate core, wherein a sufficient amount of a phenate promoting agent is added to a predetermined amount of a phenol at a reaction temperature of less than about 70 0 C. 10 The phenol consumed in the initial step may comprise up to 75 per cent of the total phenol required to make the resin. However, normally the phenol consumed in the initial step will comprise at least 33 per cent of the total required. 15 For example a third of the required phenol may be reacted in a step subsequent to an initial two thirds to form the phenate (1.00:1.00 phenate forming alkali:phenol or less) in a two step procedure. However additional steps may be used provided that approximately one third of the overall 20 phenol is reacted to the phenate core. For example in a three step process one third of the phenol may be in the form of phenate and the molar ratio of phenate forming agent:phenol may be up to approximately 2.00:1.00. A second third of phenol may be reacted with the original third 25 bringing the ratio of phenate forming agent:phenol to 1.00:1.00. A final third of phenol may finally be reacted which will be reacted without the presence of phenate forming agent. Preferably, the agent is present in at least a 30 0.1:1.0 molar ratio to the phenol. More preferably, the agent is present in a range of molar ratios of between about 0.1:1 to 2.0:1.0 to the phenol, provided that the phenate promoting agent does not exceed approximately 0.75 moles when calculated on the entire overall phenol charge. 35 Preferably, the agent is a strong base such as, for example, sodium or potassium hydroxide, but is not limited to these. Preferably, the base is of sufficient WO 00/31160 PCT/AU99/01054 -5 strength to displace the phenolic hydrogen from the phenolic group of the resin. Preferably, the reaction temperature is about 60'C. Surprisingly, it was found that when the strong 5 base was added in this first stage(s) of the reaction, the base was found to remain associated with the core component of the resin, thereby allowing any peripheral reactive phenolic groups that were subsequently condensed with the highly alkaline core to assume a relatively lower pH and 10 hence a higher reactivity. Following the initial step, the phenate is preferably reacted in aqueous solution with formaldehyde under conditions which promote a methylolation reaction rather than condensation polymerisation. 15 Conditions which promote a methylolation reaction include: (i) adding the formaldehyde to the aqueous phenate solution over a period of time; and (ii) maintaining the reaction temperature at between 50 20 70'C during the addition of formaldehyde. Optionally, a non-phenate forming base in a predetermined amount is added to the aqueous solution. Preferably, the amount of formaldehyde is at least in a 1:1 molar ratio to the phenol. More preferably, the 25 molar ratio of formaldehyde to phenol is at least 2:1. Preferably, the formaldehyde is formalin, but is in no way limited to this. Preferably, the time for the addition of formaldehyde is about 10-60 minutes. More preferably, the time for the addition of formaldehyde is 30 minutes. 30 Preferably, the reaction temperature is about 60'C. Preferably, the non-phenate forming base is a weak base such as an alkali metal carbonate although not limited to these. More preferably, the weak base is sodium carbonate. Preferably, the weak base is one which is not 35 capable of promoting the formation of phenates. Utilising these reaction conditions, the methylolation reaction pathway is promoted over the WO 00/31160 PCT/AU99/01054 -6 condensation pathway. However, if condensation agents such as sodium carbonate have been added at this stage of the reaction, it is desirable that every effort be exercised in limiting the condensation reaction such as by employing a 5 reaction temperature towards the lower end of the temperature range i.e of about 50'C. The methylolation pathway results in a product, which contains a mixture of essentially mono- and di-meric methylolated compounds, rather than phenol-formaldehyde polymers, which would be 10 formed were the condensation pathway to be favoured. The formation of such polymers causes an undesired increase in molecular weight and hence undesired increase in viscosity. Preferably, the process of the present invention further includes the steps of adding a second predetermined 15 amount of phenol to the reaction solution over a period of time, wherein the phenol is non-phenate; and raising the reaction temperature to a temperature about above 70 0 C. Preferably, the temperature is between about 80-90'C. More preferably, the reaction temperature is about 88 0 C. 20 Preferably, the period of time is about 5-15 minutes. The period of time taken for the addition of phenol is variable depending on the temperature at which the phenol is added. After this addition of phenol, a non-phenate phenol group becomes attached to the phenate core component 25 of the resin, formed in the initial core methylolation step of the reaction, thereby increasing the molecular weight of the resin in a controlled manner. Preferably, any agent used in this step is not capable of producing phenates. However, if such an agent is added, it is preferable that 30 such an agent be limited to a molar ratio of agent to overall moles of phenol added of about less than 0.1:1.0. Preferably, the process of the present invention further includes the step of maintaining the temperature at about between 80-90 0 C to allow the reaction solution to 35 reach a predetermined viscosity. Preferably, the reaction temperature is maintained at 880C until the viscosity reaches about 250-750 c.p.s. More preferably, the viscosity WO 00/31160 PCT/AU99/01054 -7 is 500 c.p.s. Preferably, any agent used in this step is not capable of producing phenates. However, if such an agent is added, it is preferably that the agent be limited to a molar ratio of agent to overall moles of phenol added 5 of about less than 0.1:1.0. Preferably, the process of the present invention further includes the steps of reducing the reaction temperature; and adding a predetermined amount of water. Preferably, the reaction temperature is reduced to about 10 between 50-70 0 C. More preferably, the reaction temperature is 60 0 C. Preferably further, the process of the present invention includes a final metholylation step, wherein a second predetermined amount of formaldehyde is added to the 15 solution over a period of time to methylolate the phenol that has been condensed, in the step immediately prior, with the high pH phenol methylol core component produced in the initial methylolation step. Preferably, the formaldehyde is formalin, but is 20 in no way limited to this. Preferably, the time for the addition of formaldehyde is about 10-60 minutes. More preferably, the time for the addition of formaldehyde is 30 minutes. Preferably, the process of the present invention 25 further includes the step of maintaining the reaction solution at the temperature at which the formaldehyde is added for an additional holding time. Preferably, the holding time is about 10-60 minutes. More preferably, the holding time period is 30 minutes. 30 Utilising these reaction conditions, the methylolation pathway is promoted over the condensation pathway. The amount of formaldehyde added in this step is such as to increase the overall formaldehyde to phenol molar ratio to fall in the range of between about 2.0:1.0 to 35 2.4:1.0. More preferably, the molar ratio is between about 2.0:1.0 to 2.2:1.0. Preferably, any agent used in this step is not capable of producing phenates. However, if such an WO 00/31160 PCT/AU99/01054 -8 agent is added, it is preferable that the agent be limited to a molar ratio of agent to overall moles of phenol added of about less than 0.1:1.0. Preferably further, the total overall amount of phenate-forming agent added at all stages 5 throughout the reaction, other than during the initial methylolation step, is limited to a molar ratio of agent to overall moles of phenol added of about less than 0.1:1. Preferably further, the process of the present invention optionally includes the steps of raising the 10 reaction temperature after the holding time period and thereafter adding a sufficient amount of a viscosity reducing agent, whereby the resin is advanced to the desired end point viscosity. Preferably, the viscosity reducing agent is selected from sucrose, melamine or urea. More 15 preferably, the viscosity reducing agent is urea. Preferably, the reaction temperature is about between 60 800C. More preferably, the reaction temperature is about between 70-750C. Preferably, the required viscosity is between about 80-500 c.p.s. The viscosity selected depends 20 on the end use. For particleboard and MDF resins the viscosity required is more likely to be 50-200 c.p.s. ,and the quantity of phenate-forming agent less than for other uses. Preferably, the process of the present invention 25 further includes the steps of cooling the reaction solution down to room temperature; and collecting the phenol formaldehyde resin produced by the process. In a preferred embodiment suitable for use with ply and LVL, the process of the present invention includes 30 the following steps: (i) adding a phenate-promoting agent to phenol in a molar ratio of between about 0.1:1.0 to 2.0:1.0 at a reaction temperature of less than 700C; (ii) reacting the phenate produced in step (i) with 35 formaldehyde in a molar ratio of between about 1:1 to 2:1 at 60'C over 30 minutes; (iii) maintaining the reaction temperature at 60'C for 30 WO 00/31160 PCT/AU99/01054 -9 minutes; (iv) adding a sufficient amount of non-phenate phenol over 5-15 minutes at 88'C to the methylol produced in step (ii) and step (iii); 5 (v) maintaining the temperature at 88 0 C to allow the viscosity to reach a viscosity of 500 c.p.s.; (vi) adding formaldehyde in a formaldehyde to overall phenol molar ratio of between about 2.0:1.0 to 2.2:1.0 to the reaction solution over 30 minutes; and 10 (vii) optionally, adding urea to the reaction solution at a reaction temperature of between about 70-75 0 C until the end point viscosity is about 400 c.p.s. According to another aspect of the present invention, there is provided a fast cure phenol-formaldehyde 15 resin, having a pH of above about 10.0, wherein the resin includes a phenate core component of high alkalinity and at least one reactive end group of lower alkalinity, wherein the resin has a solids content of less than 44%. Preferably, at least one reactive end group 20 comprises a phenolic methylol group. Preferably, the pH of the resin is about 11.0-13.5. Preferably, the resin has a solids content of between about 41-42%. Examples 25 The invention will now be further illustrated with reference to the following non-limiting examples: Example 1 Synthesis of a fast-cure phenol-formaldehyde involving two phenol addition steps 30 Sodium hydroxide solution of 46% concentration (3325.1 g) was added to phenol (3600g) and the reaction mixture allowed to self-heat for 5 minutes to approximately 60-70 0 C. Water (4300.1 g) was added with sodium carbonate (676.0 g) and the temperature of the reaction solution was 35 adjusted to 60 0 C. Formalin of 54% concentration (4254.8 g) was added to the aqueous solution over a thirty-minute period at 60 0 C. The reaction temperature was then WO 00/31160 PCT/AU99/01054 - 10 maintained at 60'C for a further thirty-minute period to facilitate the methylolation step. A further amount of phenol (2400 g) was then added over a ten-minute period and the temperature adjusted to 5 88 0 C. The reaction temperature was maintained at this higher temperature until the viscosity reached about 500 c.p.s. A further amount of water (4395.8 g) was added while reducing the temperature to 600C. The further amount of phenol may be added after 10 the methylolation step prior to raising the temperature to 88 to 90 0 C, or during the period in which the temperature is raised. If the further amount of phenol is added prior to raising the temperature, the period over which the further phenol is added is preferably longer than 5 to 15 minutes 15 and could even be as much as 60 minutes. Thus it is desirable to add further phenol over a time period of 5 to 15 minutes at a temperature above 750C and over a longer period at a lower temperature, eg. 60 minutes at 600C. Formalin of 54% concentration (3536.6 g) was added 20 over a thirty-minute period at a reaction temperature of 60 0 C. The reaction temperature was maintained at this temperature for thirty minutes. The temperature of the reaction solution was then raised to 740C to advance the viscosity to 250 c.p.s. Urea (1394.4 g) was then added and 25 the reaction temperature reduced to 720C. The resin viscosity was allowed to advance to 400 c.p.s., whereupon the resulting resin was cooled and collected. Typical analysis of the fast cure phenol formaldehyde resin produced according to the above synthetic 30 process: 1. Solids content (16 hours @ 1050C): 41.5-42.0% 2. Viscosity: 380-420 c.p.s. 3. Gelation time (min @ 1000C): 11.0-12.30 35 4. Alkalinity (to pH 4.0): 7.1-7.4% 5. Stability (@ 25'C (to double viscosity)) 7-9 days WO 00/31160 PCT/AU99/01054 - 11 Trial 1 In this Trial, the gluing properties of the resin formulation of the present invention (FC Resin) was compared with that of a fast cure commercial resin PP 1984 using 5 veneer for the construction of Laminated Veneer Lumber (LVL). The construction of the wood was using 23 x 3.0 mm P. radiata veneers, having a moisture content of 5.0%. The glue spread was 264-275 gm 2 per single glue line. The trials were conducted using veneer conditioned to 20 0 C. The 10 hot press time and temperature was 39 minutes at 185'C. The comparative results are shown in Table 1. The resin formulations for PP 1984 and FC Resin were the same as follows: 15 Resin 100.0 parts Macadamia nut shell flour 10.0 parts Wheat flour 5.0 parts Water 17.5 parts 20 Table 1 Results of the comparison of the gluing properties of PP 1984 and the resin formulation of the present invention (FC Resin) for LVL Type of Dry bond test Soak test Total resin conducted at ex-press conducted at assembly time plus 1,3 and 7 min ex-press plus (m) (chisel test-centre 1,3 and 7 mi glue line wood (broken along failure (%) centre glue line) wood failure (%) PP 1984 60, 80, 90 20, 90, 90 40 FC Resin 40, 50, 80 60, 70, 80 40 25 Summary This test is used as an indication of the cure speed of resins for the production of LVL. Upon release WO 00/31160 PCT/AU99/01054 - 12 from the hot press, the temperature of the centre glueline continues to rise for a considerable time during the transference of heat from the hotter outer veneers to the centre glueline. Therefore, results obtained by testing at 5 various times ex-press may be used as an indication as to whether subsequent pressing time can be reduced or needs to be increased. These results indicate that the cure time of the FC Resin is at approximately equal to PP 1984. However, the 10 more definitive soak test tends to indicate that the FC Resin formulation achieves an acceptable bond at one minute ex-press, whereas PP 1984 formulation does not pass, requiring an extra 2 minutes for the achievement of the same level of wood failure as the FC Resin. A pass is 50% or 15 greater wood failure. Trial 2 In this Trial, the gluing properties of the resin formulation of the present invention (FC Resin) were 20 compared with those of PP 1984 using veneer for the construction of plywood. The construction of the wood was using 7 x 2.5 mm P. radiata veneers having a moisture content of 5.0%. The glue spread was 386-397 gm2. The veneers were conditioned to 20 0 c prior to gluing. The hot 25 press time and temperature was 7 minutes at 140 0 C. The comparative results are shown in Table 2. The different resin formulations were as follows: 30 PP 1984 Resin 100.0 parts Macadamia nut shell flour 12.0 parts Wheat flour 10.0 parts Water 23.0 parts 35 FC Resin Resin 100.0 parts Macadamia nut shell flour 15.0 parts Wheat flour 10.0 parts WO 00/31160 PCT/AU99/01054 - 13 Water 25.0 parts Table 2 Results of the comparison of the gluing properties of PP 1984 and the resin formulation of the 5 present invention (FC Resin) for plywood Type of Open and total assembly 72 hour boil test resin time (min) (average 4 glue lines) vs. assembly time wood failure (%) PP 1984 5/30, 5/90, 15/30, 15/90 78, 82, 85, 80 FC Resin 5/30, 5/90, 15/30, 15/90 82, 80, 82, 83 For the attainment of a pass of glueline should achieve an average wood failure of 50% or greater. 10 Summary These results indicate that the fast cure resin of the present invention can provide bonding using P. radiata veneers equivalent to that of PP 1984, but by using a 15 greater quantity of fillers and water. Preliminary bonding trials using high density "very difficult to glue" eucalypts such as blackbutt and flooded gum, have indicated very promising results. 20 Example 2 Synthesis of a fast-cure phenol-formaldehyde involving two phenol addition steps Sodium hydroxide solution of 46% concentration (173.9g) was added to phenol (941.0g) and the reaction mixture allowed to self-heat for 5 minutes to approximately 25 60-70 0 C. Water (848.4g) was added and the temperature of the reaction solution was adjusted to 60 0 C. Formalin of 54% concentration (1112.2g) was added to the aqueous solution over a thirty-minute period at 60 0 C. The reaction temperature was then maintained at 60 0 C for a further 30 thirty-minute period to facilitate the methylolation step. A further amount of phenol (470.5g) dissolved in WO 00/31160 PCT/AU99/01054 - 14 water (64.2g) was then added over a ten-minute period and the temperature adjusted to 90'C. The reaction temperature was maintained at this higher temperature until the viscosity reached about 85 c.p.s. At this viscosity, sodium 5 carbonate (212.0g) dissolved in water (530.1g) was added while reducing the temperature to 60 0 C. Formalin of 54% concentration (722.9g) was added over a thirty-minute period at a reaction temperature of 60 0 C. The reaction temperature was maintained at this 10 temperature for thirty minutes. The temperature of the reaction solution was then further maintained at 60'C to advance the viscosity to 150 c.p.s. Urea (200.0 g) was then added and the reaction temperature was maintained at 60'C. The resin viscosity was allowed to advance to 225 c.p.s., 15 whereupon the resulting resin was cooled and collected. A typical analysis of a fast cure phenol formaldehyde resin produced according to the above process is as follows: 20 1. Solids content (16 hours @ 105 0 C): 44.5-45.5% 2. Viscosity: 220-250 c.p.s. 3. Gelation time (min @ 100 0 C): 9.00-10.00 4. Stability (@ 15'C (to double viscosity)) 6-8 days 25 Trial 3 In this trial, the gluing properties of this resin formulation was compared to that of a commercial resin (Gunei Kagaku Kogyo) of 51.0% solids content, 228 C.P. S. viscosity and a gelation time of 31min 30 sec at 100 0 C for 30 the fabrication of MDF. The MDF for the adhesion trials was of 3mm thickness. The wood furnish comprised Pinus radiata commercial MDF fibre having a wax coating of 0.8% on dry weight of fibre. The moisture content prior to resin addition was 3.5%. The application of experimental resin 35 and the commercial resin was carried out by way of airless spray injection into a closed loop blow-line of 150mm diameter. Both glue loadings were 12% on dry weight of wood WO 00/31160 PCT/AU99/01054 - 15 fibre and the sprayed furnish was approximately 10-11% after spraying prior to hot pressing between 2.5mm thickness aluminium caul plates at a hot press temperature of 196 198'C for 60 seconds. 5 Table 3 Results of the comparison of the gluing properties of Gunei Kagaku Kogyo and experimental resin of the present invention Resin Internal Modulus Modulus of Thickness Thickness type bond of Elasticity swell (2 swell (24 and MPa Rupture (MOE) HR in HR in panel (MOR) Gpa water at water at number MPa 70 0 C) % 20 0 C) % Gunei 1 Blown Blown Blown Blown Blown Gunei 2 Blown Blown Blown Blown Blown Gunei 3 0.44 61.7 4.98 18.3 14.0 FC 1 0.42 61.1 5.0 17.9 15.8 FC 2 0.54 59.2 4.8 16.2 14.0 FC 3 0.60 N/A N/A N/A 14.2 10 N/A Results not obtained After pressing between the caul plates for 90 seconds, the Gunei panels did not blow, thus indicating that the Gunei panels were incompletely cured at 60 seconds, 15 whereas the FC panels had cured within 60 seconds thereby demonstrating the faster cure speed of the FC resins. Summary These results indicate the faster curing 20 properties of the FC resin as compared to the Gunei commercial resin under identical pressing conditions. Whilst a number of properties are approximately equal for both resins, the absence of blown panels in the case of the FC resin indicates the more complete cure of the fast cure 25 resin.

WO 00/31160 PCT/AU99/01054 - 16 Overall Summary The newly developed fast cure resins have been shown to offer substantial cost reductions compared with resins used previously. These cost reductions can be 5 summarised as follows: 1. The time required for processing has been decreased by approximately 30% compared to that of previously developed fast cure resins. 2. The resin can achieve the same results without the 10 addition of expensive surfactants. 3. The resin can be extended to a greater extent using cheap fillers and yet achieve equivalent bond qualities compared to other resins. In addition, other positive aspects of producing 15 the fast cure resins of the present invention by the process disclosed herein is their "forgiving nature" with regard to the necessary accuracy of the intermediate viscosity control and proven reproducability. Performance results indicate that the curing speed of resins provided by the present 20 invention is most probably faster than that of previously used resins. In addition, for more demanding gluing requirements, the resin of the present invention can easily be modified by, for example, reducing or removing the urea content or potentially, by adding other viscosity reducing 25 agents other than urea, that may act as adhesives upon cure. The invention has been described largely with respect to resins suitable for LVL and plywood. However lower final viscosities, differing molar ratios and solids contents may be applicable for other applications such as 30 particleboard, oriented strand board (OSB) and medium density fibreboard (MDF). Those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described. It 35 is to be understood that the invention includes all such variations and modifications. The invention also includes all of the steps, features, compositions and compounds WO 00/31160 PCT/AU99/01054 - 17 referred to or indicated in this specification (unless specifically excluded) individually or collectively, and any and all combinations of any two or more of said steps or features. 5 Throughout the specification and claims, the words "comprise", "comprises" and "comprising" are used in a non exclusive sense.

Claims (21)

1. A process for producing a phenol formaldehyde resin, the process including an initial step of forming a 5 phenate core by reacting a phenol with a sufficient amount of a phenate promoting agent at a temperature of less than 70 0 C.

2. A process according to claim 1, wherein the phenol consumed in the initial step comprises from 33% to 75% of 10 the total required to produce the resin.

3. A process according to claim 1, wherein the phenate promoting agent is present in a molar ratio of at least 0.1:1.0 with respect to the phenol.

4. A process according to claim 3, wherein the molar 15 ratio of the phenate promoting agent lies in a range from 0.1:1.0 to 2.0:1.0 with respect to the phenol providing that the phenate promoting agent does not exceed a molar ratio of 0.75 with respect to the total amount of phenol required to make the resin. 20

5. A process according to any one of claims 1 to 4, wherein the phenate promoting agent is a strong base..

6. A process according to claim 1, wherein the strong base is sodium hydroxide or potassium hydroxide.

7. A process according to any one of claims 1 to 6, 25 wherein the process includes the step of reacting the phenate in aqueous solution with formaldehyde under conditions which promote a methylolation reaction rather than condensation polymerisation.

8. A process according to claim 7, wherein the 30 conditions which promote a methylolation reaction include maintaining a reaction temperature in a range from 50 to 70"C.

9. A process according to claim 7 or claim 8, wherein the conditions which promote a methylolation reaction 35 include reacting the phenate with formaldehyde at a molar ratio of at least 2:1 formaldehyde to phenol.

10. A process according to any one of claims 7 to 9, WO 00/31160 PCT/AU99/01054 - 19 wherein the conditions which promote a methylolation reaction include addition of a non-phenate forming base.

11. A process according to claim 10, wherein the non phenate forming base is a weak base. 5

12. A process according to claim 11, wherein if the weak base is sodium carbonate, the reaction temperature is maintained at about 50 0 C.

13. A process according to any one of claims 7 to 12, wherein the process includes the step of adding additional 10 phenol over a period of time and raising the reaction temperature above 70 0 C.

14. A process according to claim 13, wherein the reaction temperature is maintained in a range from 80 to 90 0 C.

15 15. A process according to claim 13, wherein the period of time lies in a range from 5 to 15 minutes.

16. A process according to any one of claims 13 to 15, wherein the reaction temperature is maintained until the aqueous solution has a viscosity in a range from 250 to 750 20 centipoise.

17. A process according to claim 16, wherein the viscosity is 500 centipoise.

18. A process according to any one of claims 13 to 17, including the step of adding additional formaldehyde under 25 conditions which promote a methylolation reaction with the additional phenol.

19. An aqueous solution of a phenol formaldehyde resin having a pH above 10 and solids content of less than 44%, the resin having a phenate core of high alkalinity and at 30 least one reactive end group of lower alkalinity.

20. An aqueous solution according to claim 19, wherein the pH lies in a range from 11 to 13.5.

21. An aqueous solution according to claim 19 or claim 20, wherein the solids content lies in a range from 41 to 42 35 per cent by weight.