JPH0525271B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to an adhesive that is suitable for bonding wood, is capable of bonding wood with a wide range of moisture content, has good workability in use, and is highly economical. . [Prior art] Currently, formaldehyde-based condensation resins are used in the production of plywood, but in order to develop sufficient adhesive performance, the veneer used must be sufficiently dried, and the moisture content of the veneer is usually lowered. It is necessary to control the content to 10% by weight or less. However, the moisture content of raw wood varies widely, and the ease with which it dries varies depending on the type of wood, so the moisture content of the veneer after drying is widely distributed, and the adhesion of the manufactured plywood. There was a problem that the force fluctuated greatly, making it impossible to obtain plywood of stable quality. Also, if excessive drying is performed, depending on the type of raw wood used, the veneer may warp or twist, making it unsuitable for normal plywood production equipment, or cracking the veneer, making it unusable. There was also a problem. In order to solve this problem, for example, when using a high moisture content veneer, we have developed a method for reducing the amount of filler such as wheat flour and water added to the adhesive, soybean flour,
Methods of adding powder, corn starch, etc., or extending the heat-pressing time have been used, but adhesive strength sufficient for practical use has not yet been achieved. Furthermore, Japanese Patent Publication No. 57-19148 discloses an adhesive made by blending an aqueous emulsion with a compound having an isocyanate group dissolved in a hydrophobic organic solvent and a surfactant, and in some cases, a formaldehyde-based condensation resin is added. It is stated that they can be used together. However, with this method,
Although it is effective for adhering wood with a high moisture content, it is not sufficient, and since the main ingredient is an aqueous emulsion, when bonding wood with a low moisture content, it takes a long time after applying the adhesive until it is pressed. Alternatively, when an adhesive is applied to wood at a high temperature, the adhesive layer tends to dry out, resulting in the problem of so-called dry adhesion, in which sufficient adhesive strength is not developed. Furthermore, since the main component is aqueous latex, there is also a problem in economic efficiency. As a result of various studies on these points, the present inventor discovered that an adhesive composition containing a formaldehyde condensation resin, an aqueous latex, an isocyanate compound, and a protein in a specific ratio has excellent performance. A patent application was filed in 1986-65850. [Problems to be Solved by the Invention] By using the above adhesive composition, it is possible to bond wood with a wide range of moisture content, and problems such as dry adhesion do not occur. was found to have poor workability. That is, the viscosity of such adhesives changes significantly over time after the formulation is adjusted, and the increase in viscosity tends to impede application control, especially under high temperatures in summer, which is a problem in terms of work.
Also, because it has thixotropic flow characteristics,
Static conditions tend to exhibit higher viscosities than those under stirring. Therefore, in areas where the flow rate is slow in the adhesive supply line or where stress is not easily applied to the adhesive, replacement with a lower viscosity adhesive is difficult to occur and the adhesive remains for a long time, which exacerbates the problem of thickening described above. It also has the problem of being easy to do. [Means for Solving the Problems] As a result of various studies to solve the above problems, the present inventor has found that urea has an extremely large improvement effect on the stability and structural viscosity of these adhesives. This discovery led to the present invention. That is, the present invention provides 100 parts by weight of a formaldehyde condensation resin containing 1 to 25% by weight of phenol, 2 to 40 parts by weight of an aqueous latex, 1 to 30 parts by weight of an isocyanate compound, and corn starch containing 60% by weight or more of prolamin. The adhesive composition contains 2 to 50 parts by weight of urea and 0.2 to 5 parts by weight of urea. The formaldehyde condensation resin containing 1 to 25% by weight of phenol in the present invention refers to a phenol formaldehyde condensation resin such as urea phenol formaldehyde cocondensation resin, melamine phenol formaldehyde cocondensation resin, and urea melamine phenol formaldehyde cocondensation resin. A condensation resin with a phenol content of 1 to 25% by weight, or a phenol formaldehyde resin or a mixture of the above phenol formaldehyde condensed resin and an amino resin such as urea formaldehyde resin, melamine formaldehyde resin, or urea melamine formaldehyde resin. A formaldehyde condensation resin mixture in which the phenol content in the mixture is 1 to 25% by weight, and usually has a nonvolatile content of 40 to 70% by weight. Preferably, a formaldehyde condensation resin obtained by mixing an amino resin with a phenol formaldehyde resin obtained by reacting 1.5 to 3.0 moles of formaldehyde per mole of phenol at a pH of 8.0 to 11.0, and more preferably, such a phenol formaldehyde resin and As an amino resin, a urea formaldehyde resin obtained by reacting 1 mole of urea with 1.0 to 1.8 moles of formaldehyde and/or a melamine formaldehyde resin obtained by reacting 1 mole of melamine with 1.5 to 3.0 moles of formaldehyde are mixed. This is the resulting formaldehyde condensation resin. The formaldehyde condensation resin used in the present invention may be a uniform dispersion system, and when prepared by mixing, the phenol resin and/or amino resin may be in powder form or an emulsion. If the phenol content is less than 1%,
The viscosity of the adhesive composition increases over time and tends to exhibit thixotropic flow, which tends to cause problems in practical use. Phenol content is 25%
If the adhesive composition of the present invention exceeds 100%, the curing of the adhesive composition according to the present invention will be extremely slow, and it will not be able to cure sufficiently under the curing conditions under which it is generally used. When the concentration decreases, partial aggregation and gelation occur, making it inconvenient to use as an adhesive. In addition, when preparing a formaldehyde-based condensation resin with a phenol content of 1 to 25% by weight by mixing, the phenol-formaldehyde resin to be used should preferably have a molar number of formaldehyde of 1.5 to 3.0 per mole of phenol. The pH of 8.0 to 11.0 is good. If the number of moles of formaldehyde per mole of phenol is less than 1.5 and/or the pH at the time of resin production is less than 8.0, the water solubility of the resulting phenolic resin will be poor, and it will be difficult to obtain a uniform adhesive composition in the present invention. The disadvantage is that it is difficult to obtain a suitable composition.
Further, when the number of moles of formaldehyde per mole of phenol exceeds 3.0, when the adhesive composition according to the present invention is prepared, the composition increases in viscosity over time and has a strong formalin odor, which causes practical problems. If the pH at the time of resin production exceeds 11.0, the curing of the adhesive composition of the present invention will be delayed, and sufficient curing will not be obtained under the curing conditions commonly used, and adhesive strength will not be developed. Depending on the mixture, the phenol content ranges from 1 to 25% by weight.
The amino resin used in preparing the formaldehyde condensation resin is a urea-formaldehyde resin obtained by reacting 1 mole of urea with 1.0 to 1.8 moles of formaldehyde, and/or a urea-formaldehyde resin obtained by reacting 1 mole of urea with 1.5 moles of formaldehyde.
It is desirable to use a melamine formaldehyde resin obtained by reacting ~3.0 mol. If formaldehyde is less than 1.8 mol per mol of urea and formaldehyde is less than 1.8 mol per mol of melamine.
If it exceeds 3.0 moles, the adhesive composition not only has a strong formalin odor but also greatly increases in viscosity over time, making it impractical. Further, if the number of moles of formaldehyde per mole of melamine is less than 1.5, a problem arises in that adhesive strength is not sufficiently developed. In the present invention, the aqueous latex refers to a latex obtained by copolymerizing a conjugated diene such as butadiene or isoprene with a monomer copolymerized therewith, such as a variety of vinyl monomers such as styrene, methyl methacrylate, or acrylonitrile, a chloroprene latex, or a butyl rubber latex. Tux, polyvinyl chloride emulsion, polybutadiene latex, ethylene vinyl acetate copolymer emulsion,
Polyvinyl acetate emulsion or these latexes contain carboxyl groups, N-methylol groups, N-alkoxymethyl groups, glycidyl groups, β
- Emulsion polymerization of at least one reactive monomer having at least one crosslinkable reactive group selected from the group consisting of a methylglycidyl group, a hydroxyl group, an amino group, an amide group, and an acid anhydride group in its side chain; It also includes so-called modified latex. Furthermore, two or more types of aqueous latexes may be used in combination. Furthermore, the blending ratio of the aqueous latex to the formaldehyde condensation resin containing 1 to 25% by weight of phenol in the present invention must be 2 to 40 parts by weight per 100 parts by weight, preferably 3 to 35 parts by weight. This is within the scope of the department. If the blending ratio is less than 2 parts by weight, adhesion to high moisture content wood will be insufficient, punctures may occur during plywood production, and only extremely low adhesion can be expected.
If the blending ratio exceeds 40 parts by weight, when using wood with low moisture content or high temperature wood, or when the blended glue is deposited for a long time after application and before cold pressing, This causes a so-called dry adhesion problem in which the adhesive layer dries and does not exhibit sufficient adhesive force. Further, the isocyanate compound referred to in the present invention may be any compound containing two or more isocyanate groups in the molecule, such as tolylene diisocyanate (TDI), 4-4'-diphenylmethane diisocyanate (MDI), hexamethylene Diisocyanate (HMDI), xylene diisocyanate (XDI), isophorone diisocyanate (IDI),
Examples include polymethylene polyphenyl polyisocyanate (Polymeric MDI). In addition, as a compound having an isocyanate group,
For example, mixtures of polyisocyanates and polyols, prepolymers, i.e. NCOs prepolymerized with polyols and excess polyisocyanate.
There is no problem in using a terminal prepolymer or a polymer obtained by adding an excessive amount of polyisocyanate to an OH-terminated prepolymer that has been polymerized in advance with an excess of polyol. The amount of isocyanate compound in the present invention is
The amount must be 1 to 30 parts by weight, preferably 2 parts by weight, per 100 parts by weight of the formaldehyde condensation resin.
~20 parts by weight. If the amount of the isocyanate compound is less than 1 part by weight, good adhesion to high moisture content wood as mentioned in the present invention cannot be expected;
If it exceeds 30 parts by weight, it is not practical because the adhesive after compounding increases in viscosity over time and is also less economical.
As for the addition method, the isocyanate compound may be added alone or after being diluted in an appropriate solvent. Alternatively, the isocyanate compound may be emulsified and added. The corn protein used in the present invention is a protein contained in corn,
A typical example is gluten meal, which is obtained as a by-product when starch is extracted from corn, and contains more than 60% by weight of prolamins.
The manufacturing method includes, for example, soaking corn in an aqueous sulfite solution and crushing it in a crusher to separate and remove the germ, and then grinding it in a crusher to separate a milky substance. Next, starch is separated from the emulsion and the remaining liquid is concentrated.
By filtering, drying, and grinding, gluten meal is obtained, usually containing 60 to 80% by weight of prolamins, with the balance consisting of starch, ash, and water. When using a large amount of corn flour with a low protein content to obtain adhesive properties for wood with a high moisture content, the fluidity of the blended glue deteriorates and the viscosity increases over time, causing problems for practical use. The prolamin content should be more than 60% by weight for this to occur. The particle size of corn protein is preferably 80 mesh or less in order to improve miscibility with the blended flour and uniform application of the blended paste. In the present invention, corn starch should be added in an amount of 2 to 50 parts by weight, preferably 5 to 30 parts by weight, per 100 parts by weight of a formaldehyde condensation resin containing 1 to 25% by weight of phenol. If the amount added is less than 2 parts by weight, the adhesion to wood with a high moisture content as mentioned in the present invention will be poor, and if it exceeds 50 parts by weight, the fluidity of the blended glue may be impaired.
A problem arises in that the applicability of the commonly used roll spreader is extremely poor. Corn protein may be added alone at the time of blending, or may be mixed in advance with a filler added at the time of blending. In the present invention, 0.2 to 5 parts by weight, preferably 0.5 to 3.0 parts by weight of urea is added to 100 parts by weight of formaldehyde resin containing 1 to 25% by weight of phenol. The addition of urea not only suppresses the conventionally known increase in viscosity of adhesive compositions over time, but also improves fluidity when the stress applied to the adhesive is small, making it less likely to stagnate in equipment. There is an advantage. It is well known that urea has the effect of reducing free formalin, for example, but this advantage of the present invention was completely unknown until now, and was discovered for the first time by the present inventor. . 1 to 25% by weight of phenol
If less than 0.2 parts by weight of urea is added to 100 parts by weight of the water-soluble formaldehyde resin contained, the above-mentioned advantages will not be obtained, and if more than 5% by weight is added, the water-resistant adhesive strength will decrease. In carrying out the present invention, a method of adding and mixing an aqueous latex, an isocyanate compound, corn protein, urea, a commonly used filler such as wheat flour, rice flour, and talc, water, and a hardening agent to a formaldehyde-based condensation resin. will be adopted. The mixing order is not particularly limited, and the stirring time during mixing, the finished viscosity of the blended composition, etc. may be controlled under the same conditions as in a normal method. In the practice of the present invention, in addition to wheat flour as a bulking agent conventionally used in plywood production, coconut flour, walnut flour, barley flour, rice flour, cornstarch, wood flour, talc, clay, etc. can be used. . Furthermore, polyvinyl alcohol added for the purpose of improving temporary adhesion, a water-retaining polymer compound added to prevent dry adhesion, and a deliquescent inorganic substance may be added. Further, the amount of adhesive composition applied and bonding conditions such as cold pressure and hot pressure can all be the same as usual conditions. The fluidity of the compounded glue obtained by the present invention is equivalent to that of a commonly used adhesive prepared by adding an extender, water, a hardening agent, etc. to a formaldehyde-based condensation resin.
Can be used with equipment such as spreaders and presses. [Example] Next, the present invention will be explained with reference to an example. Note that parts and percentages are based on weight unless otherwise specified. Reference example 1 94 parts phenol, 37% formalin 200 parts 48%
The pH was adjusted to 10.5 with an aqueous solution of caustic soda, and the reaction was carried out at 85° C. for 2 hours with stirring, followed by cooling. The nonvolatile content of the obtained phenolic resin was 47.2%. This resin is hereinafter abbreviated as PF1. Reference Example 2 120 parts of urea and 325 parts of 37% formalin were adjusted to pH 7.5 with a 20% aqueous solution of caustic soda, heated with stirring and reacted at 85°C for 30 minutes, and then adjusted to PH 5.0 using a 40% aqueous acetic acid solution. The mixture was reacted at 85°C for 30 minutes.
Then, adjust the pH to 7.0 with a 20% aqueous solution of caustic soda, add 45 parts of urea, react at 75℃ for 30 minutes, and then adjust the pH to 7.0.
was adjusted to 8.0 and cooled. The nonvolatile content of the obtained urea resin was 52.3%. This resin is hereinafter abbreviated as UF1. Reference Example 3 250 parts of melamine and 450 parts of 37% formalin were adjusted to pH 10.0 with a 20% aqueous sodium hydroxide solution, heated with stirring, reacted at 85°C for 2 hours, and then cooled. The nonvolatile content of the obtained melamine resin was 57.7%. This resin is hereinafter abbreviated as MF1. Reference example 4 94 parts phenol, 37% formalin 285 parts 48%
The pH was adjusted to 11.0 with aqueous caustic soda solution, and the reaction was carried out at 85°C for 2 hours with stirring, followed by cooling. The nonvolatile content of the obtained phenolic resin was 43.7%. This resin is hereinafter abbreviated as PF2. Reference Example 5 120 parts of urea and 355 parts of 37% formalin were adjusted to pH 7.5 with a 20% aqueous solution of caustic soda, heated to 85°C with stirring.
After reacting for 30 minutes at 40°C, using an acetic acid aqueous solution
The pH was adjusted to 5.0, and the reaction was carried out at 85°C for 30 minutes. Then adjust the pH to 7.0 with 20% caustic soda aqueous solution,
After adding 22 parts of urea and reacting at 75°C for 30 minutes,
The pH was adjusted to 8.0 and cooled. The nonvolatile content of the obtained urea resin was 50.1%. The following resin is UF2
It is abbreviated as Reference Example 6 250 parts of melamine and 585 parts of 37% formalin were adjusted to pH 10.0 with a 20% aqueous sodium hydroxide solution, heated with stirring, reacted at 85°C for 2 hours, and then cooled. The nonvolatile content of the obtained melamine resin was 55.3%. This resin is hereinafter abbreviated as MF2. Reference Examples 7 to 9 Each mixture having the composition shown in Table 1 was charged into a tank equipped with a stirrer to prepare a monomer emulsion. In an autoclave equipped with a stirrer, 32 parts of water, 0.1 part of tetrasodium salt of ethylenediaminetetraacetic acid, 0.1 part of sodium lauryl sulfate, and 0.2 parts of potassium persulfate were charged, and 10% of the monomer emulsion was added.
was transferred to an autoclave, heated to 80°C, and reacted for 1 hour. After 1 hour, add 0.8 parts of potassium persulfate to water.
After charging with 20 parts, the remaining monomer emulsion was added continuously to the autoclave over a period of 4 hours. During this time, the autoclave was kept at 80°C. After continuing the reaction at 80° C. for an additional hour, residual monomers were removed by steam distillation, and aqueous ammonia was added to adjust the pH of the latex to 9.0. The latex synthesized according to Reference Example 7 below is referred to as latex A.
The latex synthesized according to Reference Example 8 is called Latex B, and the latex synthesized according to Reference Example 9 is called Latex C.

[Table] Examples Reference examples 1 to 1 as formaldehyde-based condensation resins
PF1, PF2, UF1, UF2, MF1 synthesized in 6.
MF2, latexes A, B, and C synthesized in Reference Examples 7 to 9 as aqueous latexes, CR-300 (manufactured by Mitsui Nisso Urethane Co., Ltd.) as an isocyanate compound, and gluten meal (Prolamin 70, manufactured by Shikishima Cornstarch Co., Ltd.) as corn starch. %
containing) crushed to 80 mesh or less, urea,
Flour as a filler (Nippon Flour Mills Co., Ltd.),
Table using water and ammonium chloride as hardening agent.
Adhesive compositions were prepared by mixing in the proportions shown in Tables 2 to 7. 1.0mm+2.0mm+1.0 using these adhesive compositions
4 mm plywood with 1 mm veneer construction (lauan veneer, moisture content below 4% and 20-25%), coating amount 370 g/m ² (both sides), cold pressure 12 Kg/cm ² for 20 minutes, hot pressure 10 Kg/cm ² , 117℃
It was manufactured under the conditions of 60 seconds, and its adhesive strength as Type 1 plywood was measured based on the Japanese Agricultural Standards. When plywood is manufactured with a veneer moisture content of 4% or less, cold pressing immediately after applying the adhesive composition to the veneer, followed by hot pressing (indicated as 4%-1 in the table) and at 60℃ Evaluation was performed using two methods: applying the adhesive composition to a preheated veneer, leaving it for 30 minutes before cold pressing, and performing cold pressing and hot pressing (indicated as 4%-2 in the table). . In addition, the ratio of the viscosity immediately after adjustment to the viscosity after being left at 35°C for 3 hours is used as a measure of the viscosity of the adhesive composition, and the automatic rotating viscosity manufactured by Kyowa Kagaku Co., Ltd. is used as a measure of fluidity under low stress. The yield viscosity was measured using a meter. The results are shown in Tables 2 to 7. In adjusting the adhesive composition, the amounts of the filler and water were varied and measured using Visco Tester UT-02 manufactured by Rion Co., Ltd., and adjusted to 18 to 23 poise.

【table】

[Table] Table 2 is an example of evaluating the phenol content in the formaldehyde condensation resin.If the phenol content is less than the range of the present invention, the yield viscosity is high and the fluidity under low stress is poor. Furthermore, if the phenol content exceeds the range of the present invention, sufficient adhesive strength will not be developed.

【table】

【table】

【table】

[Table] Table 4 is an example in which the amount of the isocyanate compound added was varied and evaluated. When the amount of the isocyanate compound was less than the range of the present invention, the adhesion strength with high moisture content veneer was low; If the amount added exceeds the range of the present invention, the adhesive composition will greatly increase in viscosity.

【table】

【table】

【table】

[Table] Table 6 is an evaluation example in which the amount of urea added was changed.
When the yield viscosity is high, the viscosity increases significantly, and when the range of the present invention is exceeded, the water-resistant adhesive strength decreases.

【table】

[Table] Table 7 shows an example in which the types of formaldehyde-based condensation resins were varied and satisfactory results were obtained for each evaluation item within the scope of the present invention. However, PF2
It is better to use PF1, and UF1 is better than UF2.
MF1 tends to have a lower yield viscosity and less thickening than MF2.
[Effects of the Invention] The adhesive composition of the present invention has excellent performance in bonding high moisture content wood, and it is possible to produce high quality plywood even when using high moisture content veneer. In addition, even if a veneer with a low moisture content is used or a veneer with a relatively high temperature is used, the problem of so-called dry adhesion is unlikely to occur. That is, it has the advantage of being applicable to wood with a wide range of moisture content, which is of great significance when used in actual plywood production. Furthermore, the adhesive composition of the present invention has excellent workability, such as a small change in the viscosity of the compounded glue over time, and extremely good applicability of the compounded glue to veneers, and has fluidity that is better than that of conventional adhesives. It also has the characteristic that it is equivalent to formaldehyde-based resin and can be applied to current plywood production lines. Furthermore, since a formaldehyde-based condensation resin can be used as the main component in the formulation, it is effective in reducing the cost of the compounded glue, and is economical enough to enable practical use in plywood production. Further, the formaldehyde-based condensation resin can be selected according to the required water resistance, and by selecting an appropriate condensation resin, it is also possible to optimize the cost of the blended glue.

Claims (1)

[Scope of Claims] 1. Corn containing 2 to 40 parts by weight of an aqueous latex, 1 to 30 parts by weight of an isocyanate compound, and 60 parts by weight or more of prolamin, based on 100 parts by weight of a formaldehyde condensation resin containing 1 to 25 parts by weight of phenol. 2 to 50 parts by weight of protein, urea
An adhesive composition characterized in that it contains 0.2 to 5 parts by weight. 2. The formaldehyde condensation resin containing 1 to 25% by weight of phenol is a mixture of phenol formaldehyde resin and amino resin obtained by reacting 1 mole of phenol with 1.5 to 3.0 moles of formaldehyde at a pH of 8.0 to 11.0. An adhesive composition according to claim 1. 3. The amino resin is a urea formaldehyde resin obtained by reacting 1 mole of urea with 1.8 moles or less of formaldehyde, and/or a melamine formaldehyde resin obtained by reacting 1 mole of melamine with 1.5 to 3.0 moles of formaldehyde. An adhesive composition according to claim 2.