1 Test purpose
In the production of plywood, the rubberized veneer is aged, the glue still maintains its fluidity, and then pre-pressed to dewater the glue, and the adjacent veneers are initially bonded, so in the subsequent operation, the bundling The boards can be neatly arranged to avoid displacement. Current versatile adhesives require longer aging times and pre-compression times to achieve satisfactory pre-compression bonding strength, or a satisfactory pre-compression characteristic even if a suitable aging time is provided. Therefore, it is desirable to find an adhesive formulation that can reduce the aging time and pre-pressing time while achieving satisfactory pre-compression bonding strength.
2 Mechanism and process requirements
2.1 Mechanism
In production, the aging time and pre-pressing characteristics of the phenolic resin adhesive are directly related to the ability of the filler and the resin to retain or lose moisture. It has been found that phenolic resin can reduce the aging time after adding alkali-treated starch with higher branching (more than 75% of amylopectin in total starch), but still maintain sufficient fluidity during aging. At the same time, the pre-compression characteristics of the glue are improved, and the curing process is rarely affected. The above method is quite different from the conventional starch modified adhesive. First, in the conventional starch-modified adhesive, the dispersion of the starch component has no decisive relationship with the amount of alkali, temperature, mixing speed, ratio of starch to water, mixing time, etc., and thus attempts to control the performance of the glue by the above conditions, often Can not achieve the desired results. The glue prepared by the formula has a decisive relationship with the above factors, and can effectively control the quality of the glue by adjusting the above-mentioned rubber adjusting conditions; secondly, the formula can obtain a fast curing adhesive, balancing the contradictory factors in the operation, so that The aging time has a long tolerance and good pre-pressure effect. Third, the formula can improve the pre-compression performance of any phenolic resin adhesive for plywood. According to past experience, in order to improve the pre-compression bonding strength, the resin needs to be greatly improved, and this requirement is greatly reduced. It should be noted that if the free formaldehyde content exceeds 5% of the solid gum amount, the dispersion of the starch is changed and the efficiency is lowered.
2 . 2 glue adjustment process requirements
The amylopectin is first combined with from 2% to 20% by weight of the alkali metal hydroxide in water, the amount of water being determined by the desired concentration of the mixture in the operation and the solids content of the final adhesive. Usually, the solid content of the adhesive is from 10% to 70% by weight, preferably from 35% to 45%. Specifically, in the pretreatment stage, at least 50% of the total water should be combined with amylopectin and an alkali metal hydroxide. In the pretreatment stage, there are three variable parameters that interact with each other, which are the mixing time, temperature, and alkali metal hydroxide concentration. The dispersion of the pretreated high amylopectin increases with increasing water temperature, mixing time and alkali metal hydroxide content, making it easier to achieve a steady state in each step than in the treatment of low amylopectin. In actual use, when the water temperature in winter is low, the mixing time can be increased with the alkali metal hydroxide or both to compensate; in summer, when the water temperature is high, the opposite method can be used. The use of preheated water further reduces mixing time and alkali metal hydroxide usage. Adhesives that use general starch modification do not have this flexibility.
3 Recipe components and performance requirements
3. 1 performance requirements of each component
Phenolic Resin: Any basic phenolic resin condensate may be used, and the free aldehyde content does not exceed 5% of the resin solids. It is preferably prepared from phenol and formaldehyde (37% or 50% solution), but 15% of the amount of phenol can also be replaced by cresol, xylenol or polyphenylphenol.
Starch: This formula uses unrefined, semi-refined and refined natural starch, which contains at least 75% amylopectin in its molecular structure, such as potato, yam, sweet potato, tapioca starch, corn starch and the like. The dispersion of starch in lye depends on its molecular structure. The molecules of hyperbranched or amylopectin are generally heavier, easier to disperse in aqueous solution to form high viscosity, and have better stability. Under conditions, water dispersion is easier than amylose. Therefore, the higher the amylopectin content, the larger the branching structure, the more suitable it is for the phenolic resin adhesive of plywood.
Base: alkali metal hydroxide.
Others: Commonly used fillers include clay, talc, white powder, calcite, etc., cellulosic materials such as wood flour, bark powder, nut shell powder and the like.
The final component contains 5 to 50 parts by weight of high amylopectin, 5 to 25 parts of filler and 100 parts of phenolic resin solids. Other commonly used additives such as fillers, curing agents, dyes, etc. may also be added to the size component.
3. 2 recipe example
This formula uses unrefined potato starch (78% amylopectin in total starch) and granulated residue after corncob is made into furfural. These granules can pass through 100 mesh mesh; the phenolic resin used is solid content. 40克的酚酚的溶液。 The resin is used at a temperature of 21 ° C, using a Mac Michael viscometer, the viscosity of the No. 6 hanging wire is 10 2, the phenolic resin is 1.0 gram of phenol and about 2.0. The molar formaldehyde is polycondensed in a solution of 0.75 mole of Na OH, and Na OH is added successively at 0.15, 0.30, 0.330, respectively, as shown in the following table.
Example formula table formula weight
Water (at 18 to 24 °C) 597
Filler 2 35
Unrefined potato starch mix 2 min 57
Phenolic resin, aqueous mixing 2 min 1 36
50% Na OH aqueous solution mixed 2 5min 6 0
Liquid phenolic resin mixed for 5min 1 2 2 1
In the production of plywood, the rubberized veneer is aged, the glue still maintains its fluidity, and then pre-pressed to dewater the glue, and the adjacent veneers are initially bonded, so in the subsequent operation, the bundling The boards can be neatly arranged to avoid displacement. Current versatile adhesives require longer aging times and pre-compression times to achieve satisfactory pre-compression bonding strength, or a satisfactory pre-compression characteristic even if a suitable aging time is provided. Therefore, it is desirable to find an adhesive formulation that can reduce the aging time and pre-pressing time while achieving satisfactory pre-compression bonding strength.
2 Mechanism and process requirements
2.1 Mechanism
In production, the aging time and pre-pressing characteristics of the phenolic resin adhesive are directly related to the ability of the filler and the resin to retain or lose moisture. It has been found that phenolic resin can reduce the aging time after adding alkali-treated starch with higher branching (more than 75% of amylopectin in total starch), but still maintain sufficient fluidity during aging. At the same time, the pre-compression characteristics of the glue are improved, and the curing process is rarely affected. The above method is quite different from the conventional starch modified adhesive. First, in the conventional starch-modified adhesive, the dispersion of the starch component has no decisive relationship with the amount of alkali, temperature, mixing speed, ratio of starch to water, mixing time, etc., and thus attempts to control the performance of the glue by the above conditions, often Can not achieve the desired results. The glue prepared by the formula has a decisive relationship with the above factors, and can effectively control the quality of the glue by adjusting the above-mentioned rubber adjusting conditions; secondly, the formula can obtain a fast curing adhesive, balancing the contradictory factors in the operation, so that The aging time has a long tolerance and good pre-pressure effect. Third, the formula can improve the pre-compression performance of any phenolic resin adhesive for plywood. According to past experience, in order to improve the pre-compression bonding strength, the resin needs to be greatly improved, and this requirement is greatly reduced. It should be noted that if the free formaldehyde content exceeds 5% of the solid gum amount, the dispersion of the starch is changed and the efficiency is lowered.
2 . 2 glue adjustment process requirements
The amylopectin is first combined with from 2% to 20% by weight of the alkali metal hydroxide in water, the amount of water being determined by the desired concentration of the mixture in the operation and the solids content of the final adhesive. Usually, the solid content of the adhesive is from 10% to 70% by weight, preferably from 35% to 45%. Specifically, in the pretreatment stage, at least 50% of the total water should be combined with amylopectin and an alkali metal hydroxide. In the pretreatment stage, there are three variable parameters that interact with each other, which are the mixing time, temperature, and alkali metal hydroxide concentration. The dispersion of the pretreated high amylopectin increases with increasing water temperature, mixing time and alkali metal hydroxide content, making it easier to achieve a steady state in each step than in the treatment of low amylopectin. In actual use, when the water temperature in winter is low, the mixing time can be increased with the alkali metal hydroxide or both to compensate; in summer, when the water temperature is high, the opposite method can be used. The use of preheated water further reduces mixing time and alkali metal hydroxide usage. Adhesives that use general starch modification do not have this flexibility.
3 Recipe components and performance requirements
3. 1 performance requirements of each component
Phenolic Resin: Any basic phenolic resin condensate may be used, and the free aldehyde content does not exceed 5% of the resin solids. It is preferably prepared from phenol and formaldehyde (37% or 50% solution), but 15% of the amount of phenol can also be replaced by cresol, xylenol or polyphenylphenol.
Starch: This formula uses unrefined, semi-refined and refined natural starch, which contains at least 75% amylopectin in its molecular structure, such as potato, yam, sweet potato, tapioca starch, corn starch and the like. The dispersion of starch in lye depends on its molecular structure. The molecules of hyperbranched or amylopectin are generally heavier, easier to disperse in aqueous solution to form high viscosity, and have better stability. Under conditions, water dispersion is easier than amylose. Therefore, the higher the amylopectin content, the larger the branching structure, the more suitable it is for the phenolic resin adhesive of plywood.
Base: alkali metal hydroxide.
Others: Commonly used fillers include clay, talc, white powder, calcite, etc., cellulosic materials such as wood flour, bark powder, nut shell powder and the like.
The final component contains 5 to 50 parts by weight of high amylopectin, 5 to 25 parts of filler and 100 parts of phenolic resin solids. Other commonly used additives such as fillers, curing agents, dyes, etc. may also be added to the size component.
3. 2 recipe example
This formula uses unrefined potato starch (78% amylopectin in total starch) and granulated residue after corncob is made into furfural. These granules can pass through 100 mesh mesh; the phenolic resin used is solid content. 40克的酚酚的溶液。 The resin is used at a temperature of 21 ° C, using a Mac Michael viscometer, the viscosity of the No. 6 hanging wire is 10 2, the phenolic resin is 1.0 gram of phenol and about 2.0. The molar formaldehyde is polycondensed in a solution of 0.75 mole of Na OH, and Na OH is added successively at 0.15, 0.30, 0.330, respectively, as shown in the following table.
Example formula table formula weight
Water (at 18 to 24 °C) 597
Filler 2 35
Unrefined potato starch mix 2 min 57
Phenolic resin, aqueous mixing 2 min 1 36
50% Na OH aqueous solution mixed 2 5min 6 0
Liquid phenolic resin mixed for 5min 1 2 2 1
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