JP2018145381A - Manufacturing method of methylenated melamine-formaldehyde initial condensate for expanded body, and manufacturing method of melamine resin expanded body using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of a methylenated melamine-formaldehyde initial condensate for expanded body extremely good in storage stability and a manufacturing method of a melamine resin expanded body based on the composition, having light weight, rich in plasticity or elasticity, and in which an internal shape is porous.SOLUTION: There is provided a manufacturing method of a methylenated melamine-formaldehyde initial condensate for expanded body obtained by a primary reaction by adding a basic catalyst to a solution containing melamine monomer, formaldehyde and no alcohol and heating them, then a secondary reaction by adding an acidic catalyst and heating them.SELECTED DRAWING: None

Description

  The present invention relates to a method for producing a methyleneated melamine-formaldehyde initial condensate for foam and a method for producing a melamine resin foam using the same.

  By reacting the melamine monomer with formaldehyde in the presence of a catalyst, a methylol melamine as a precondensate is obtained, and when the reaction proceeds further, the precondensate crosslinks in the form of a network, resulting in a melamine resin. Can be manufactured. Melamine resins have high strength and hardness and are excellent in water resistance and weather resistance, and are therefore preferably used for woodworking adhesives and daily necessities such as tableware.

  Moreover, immediately after obtaining methylol melamine which is a precondensate, a foaming agent is added and it heats, A fine bubble is generated and the melamine resin foam which has a porous shape can be manufactured. Since this foam is light and flexible, it is used as a cushion sponge and mat for bedding, as well as a building material such as a heat insulating material and a sound absorbing material, and a cleaner sponge for washing tableware and the like.

  Conventionally, extensive research has been conducted on melamine resin foams. Specifically, a melamine resin foam characterized by foaming a resin composition containing a melamine formaldehyde condensate, a foaming agent and an isocyanate is known (Patent Document 1). This foam solves the brittleness problem without impairing the flame retardancy and thermal conductivity inherent to the melamine resin foam.

JP 7-157590 A

  However, methylol melamine, which is a precondensate, has a problem that its storage stability is very poor because it rapidly thickens after being left at room temperature for about 1 hour. Therefore, the foam must be produced immediately after obtaining the precondensate, and it has been necessary to pay close attention to its handling. Moreover, in order to improve the storage stability, there is a method of adding alcohol in advance, but since the reactivity is lowered, the final foam tends to be slightly inferior in flexibility and elasticity. In addition, since an explosion-proof manufacturing facility is required, there is room for further study of the manufacturing method.

  The problem to be solved by the present invention is to provide a process for producing a methyleneated melamine-formaldehyde precondensate for foams, which has extremely good storage stability. Moreover, the manufacturing method of the melamine resin foam which is lightweight based on the said composite, is rich in a softness | flexibility and elasticity, and an internal shape is porous.

  The present invention is obtained by adding a basic catalyst to an aqueous solution containing melamine monomer and formaldehyde and not containing alcohol and heating to cause a primary reaction, and then adding an acidic catalyst and heating to cause a secondary reaction. It is a manufacturing method of the methyleneated melamine-formaldehyde initial stage condensate for foams characterized by these.

  The methyleneated melamine-formaldehyde initial condensate for foams according to the present invention has an effect that the storage stability is extremely good. Moreover, the melamine resin foam manufactured based on the said synthetic | combination is lightweight, is rich in a softness | flexibility and elasticity, and there exists an effect that an internal shape is porous.

<Methylene melamine-formaldehyde initial condensate>
In the present invention, a methylated melamine-formaldehyde initial condensate (A) is synthesized. The component (A) can be synthesized by a two-step reaction. The primary reaction is the synthesis of methylol melamine as a precondensate, which can be obtained by adding a basic catalyst to an aqueous solution containing melamine monomer and formaldehyde and no alcohol and heating. Formaldehyde is preferably blended as formalin in order to improve workability.

  Moreover, you may mix | blend another aldehyde within the range which does not impair the effect of this invention. Examples of other aldehydes include paraformaldehyde, acetaldehyde, terephthalaldehyde, propionaldehyde, acrolein, benzaldehyde, trioxane, dicyclopentadiene, furfural and the like.

  The blending ratio of the melamine monomer and aldehydes containing formaldehyde is preferably 1: 1 to 5 and particularly preferably 1: 2 to 4 in terms of molar ratio. By blending within this range, the molecular structure of the finally produced melamine resin becomes a three-dimensional network, and therefore mechanical properties such as flexibility and strength tend to be remarkably improved.

  Examples of the basic catalyst include metal hydroxide and ammonia. Before the reaction of the primary reaction, a basic catalyst is added to adjust the pH of the aqueous solution, and the pH at that time is preferably 8 or more and less than 11, and particularly preferably 8.5 or more and less than 10. . By being within this range, methylolmelamine can be efficiently synthesized.

  The reaction temperature of the primary reaction is preferably 80 ° C. or higher and lower than 110 ° C., particularly preferably 85 ° C. or higher and lower than 105 ° C. Furthermore, the reaction time is preferably 0.5 hours or more and less than 4 hours, particularly preferably 1 hour or more and less than 3 hours. There exists a tendency which can improve storage stability by synthesize | combining on these reaction conditions.

  As the reaction solvent, water is usually used, but other solvents may be used as long as the effects of the present invention are not impaired. However, alcohols such as methanol and ethanol cannot be used.

  Next, as a secondary reaction, methylol melamine synthesized by the primary reaction is further subjected to a methylation reaction to synthesize a methylated melamine-formaldehyde initial condensate. Specifically, after completion of the primary reaction, it can be obtained by adding an acidic catalyst to a basic aqueous solution containing methylolmelamine and heating.

  Examples of the acidic catalyst include hydrochloric acid, sulfuric acid, nitric acid, formic acid, oxalic acid, paratoluenesulfonic acid amide and the like. Before the reaction of the secondary reaction, an acidic catalyst is added to adjust the pH of the aqueous solution, and the pH at that time is preferably 6 or more and less than 8, and preferably 6.5 or more and less than 7.5. Particularly preferred. By being in this range, a methyleneated melamine-formaldehyde initial condensate can be efficiently synthesized.

  The reaction temperature of the secondary reaction is preferably 50 ° C. or higher and lower than 80 ° C., and particularly preferably 55 ° C. or higher and lower than 75 ° C. Furthermore, the reaction time is preferably 0.3 hours or more and less than 3 hours, and particularly preferably 0.5 hours or more and less than 2 hours. There exists a tendency which can improve storage stability by synthesize | combining on these reaction conditions.

  After completion of the secondary reaction, a basic catalyst can be added as necessary. In that case, the pH is preferably 8 or more and less than 11. In this invention, after synthesize | combining the said (A) component, various additives can be added further and a foam can be manufactured. Examples of the additive include a foaming agent (B), an emulsifier (C), and a curing agent (D).

<Foaming agent>
In the present invention, the foaming agent (B) is used. The component (B) is a chemical substance in which fine bubbles are generated by heating, and a molded article having a porous shape can be produced by dispersing in the component (A).

  The component (B) includes various organic foaming agents and inorganic foaming agents. Examples of the organic foaming agents include hydrocarbons such as various isomers of pentane and various isomers of hexane, azodicarbonamide and hydra. Amide compounds such as zodicarbonamide and the like, and examples of the inorganic foaming agent include fluorine compounds such as hydrofluoroether and hydrofluorocarbon, and carbonate compounds such as sodium hydrogen carbonate and ammonium carbonate.

  The blending ratio of the component (B) is preferably 1 to 100 parts by weight and particularly preferably 5 to 50 parts by weight based on 100 parts by weight of the component (A) in terms of solid content. . By blending within this range, the foam can be reduced in weight, and the cell shape in the foam tends to be uniform.

<Emulsifier>
In the present invention, the emulsifier (C) is used. Examples of the component (C) include those that are anionic, cationic, and amphoteric, and those that are nonionic. Among these, it is preferable to use an anionic surfactant. Specific examples include those obtained by esterifying alkylsulfonic acid, alkylbenzenesulfonic acid, phenolsulfonic acid, sulfuric acid and the like.

  The blending ratio of the component (C) is preferably 1 to 30 parts by weight and particularly preferably 3 to 20 parts by weight based on 100 parts by weight of the component (A) in terms of solid content. . By blending within this range, the cell diameter of the foam can be kept within a certain range, so that the bias of the cavity can be suppressed and flexibility can be imparted.

<Curing agent>
In the present invention, a curing agent (D) is used. By mix | blending the said (D) component, the hardening reaction of the said (A) component after a synthesis | combination can be accelerated | stimulated. As the component (D), an acidic aqueous solution is preferably used. Specific examples include formic acid, sulfuric acid, phosphoric acid, oxalic acid, hydrochloric acid, and acetic acid.

  The blending ratio of the component (D) is preferably 0.1 to 20 parts by weight and preferably 1 to 10 parts by weight based on 100 parts by weight of the component (A) in terms of solid content. Particularly preferred. By mix | blending within this range, the said (A) component can be hardened | cured efficiently.

  A known method can be used as a method for producing the foam. Examples thereof include a method in which the components (A) to (D) are stirred to obtain a mixed solution, which is then poured into an appropriate mold, and foamed by heating or irradiation with microwaves.

  In addition, in the present invention, various additives such as antioxidants, preservatives, tackifiers, and plasticizers are included in the synthesis of the methyleneated melamine-formaldehyde initial condensate and the production of the melamine resin foam. Also good.

  EXAMPLES Hereinafter, although an Example and a comparative example are given and demonstrated in detail about this invention, a specific example is shown and it does not specifically limit to these.

<Synthesis of Methyleneated Melamine-Formaldehyde Initial Condensate>
Example 1
120 parts by weight of melamine monomer and 210 parts by weight of 37% formalin are charged into a separable flask equipped with a stirrer, reflux condenser and thermometer, and a 48% sodium hydroxide aqueous solution having a pH of 9 is added as a basic catalyst. The reaction was carried out at 95 ° C. for 90 minutes. Then, paratoluenesulfonic acid amide was added so that pH might be set to 7.2, and reaction was performed at 70 degreeC over 45 minutes. After completion of the reaction, the mixture is naturally cooled, and when the temperature drops to 60 ° C., a 48% sodium hydroxide aqueous solution is added again so that the pH becomes 9.0, and excess water is added until the solid content becomes 75%. Removal and natural cooling again gave a methyleneated melamine-formaldehyde precondensate.

<Synthesis of methylol melamine>
(Comparative Example 1)
120 parts by weight of melamine monomer and 210 parts by weight of 37% formalin are charged into a separable flask equipped with a stirrer, reflux condenser and thermometer, and a 48% sodium hydroxide aqueous solution having a pH of 9 is added as a basic catalyst. The reaction was carried out at 95 ° C. for 90 minutes. After completion of the reaction, the mixture is naturally cooled, and when the temperature drops to 60 ° C., a 48% sodium hydroxide aqueous solution is added again so that the pH becomes 9.0, and excess water is added until the solid content becomes 75%. After removal and natural cooling again, methylolmelamine was obtained.

  The colorless and transparent composites obtained in the above Examples and Comparative Examples were placed in a 100 mL plastic bottle with a lid, stored at 30 ° C., and evaluated for physical properties after a certain period of time. The results are shown in Table 1.

<Storage stability (visual)>
The appearance of the composite was visually observed after 1 hour, 1 day, 3 days, and 5 days from the start of storage.
○: It remains colorless and transparent.
Δ: Turbidity is observed in part.
X: The whole is cloudy.

<Storage stability (viscosity)>
From the start of storage, the viscosity of the composite was measured after 1 hour, 1 day, 3 days, and 5 days. Specifically, with a BM spindle viscometer (Toki Sangyo Co., Ltd.), the composition was put into a cell kept at 30 ° C. No. 4 spindle was inserted, and the viscosity when the spindle was rotated at 60 rpm was measured. * Indicates that measurement was not possible because the viscosity was extremely high.

  Moreover, after putting the composite obtained by said Example and comparative example into the plastic bottle with a lid | cover and preserve | saving for 1 hour at 30 degreeC, the melamine resin foam was manufactured by the following mixing | blendings. Hereinafter, all blending amounts are in terms of solid content.

<Manufacture of melamine resin foam>
(Example 2)
As component (A), 75 parts by weight of the methyleneated melamine-formaldehyde initial condensate synthesized in Example 1;
As component (B), 10.5 parts by weight of CF ₃ (CF ₂ ) ₅ H (boiling point 71 ° C., surface tension 13.4 mN / m), CF ₃ CH ₂ CF ₂ CH ₃ (boiling point 40 ° C., surface tension 15) 0.0 mN / m) and 15 parts by weight of n-hexane,
As component (C), 3 parts by weight of sodium dodecylbenzenesulfonate and 4 parts by weight of sodium polyoxyethylene lauryl ether sulfate,
As a component (D), 2 parts by weight of formic acid was blended, put into a disc turbine mixer, and stirred at a rotational speed of 3000 rpm for 30 seconds to obtain a mixed solution. Then, 35 g of the mixed solution was poured into a 2 L polycup, heated at 160 ° C. for 10 minutes to foam, then demolded and further cured at 200 ° C. for 30 minutes to be completely cured, and the melamine resin of Example 2 A foam was obtained.

(Comparative Example 2)
As the component (A), except that the methylol melamine synthesized in Comparative Example 1 was used, it was performed in the same manner as in Example 2. However, since significant thickening occurred, a normal foaming phenomenon did not occur. A foam could not be produced due to the formation of a non-uniform bulky solid.

  About the melamine resin foam obtained in Example 2, the test piece was produced and the physical property evaluation was performed. The results are shown in Table 2.

<Preparation of test piece>
The inside of the foam was cut out so as not to include the surface of the obtained melamine resin foam, and adjusted to a size of 50 mm × 50 mm × 50 mm to prepare a test piece.

<Density>
The weight of the test piece was measured, and the density (g / cm ³ ) was calculated.

<Cell diameter>
Using a microscope (Keyence Co., Ltd.), each specimen was observed at a magnification of 750, and 5 samples of cells were randomly selected for each field of view, and a total of 6 fields of images of 30 samples were output. . The maximum value of the diameter of each specimen cell was defined as the cell diameter of each specimen, and the average value of the cell diameters of 30 specimens was defined as the cell diameter (μm) of the test piece.

<25% compressive strength>
Using a universal testing machine (Shimadzu Corporation) at a test speed of 1 mm / min, the strength (kPa) when compressed by 25% in the thickness direction with reference to the original thickness (50 mm) of the test piece ) Was measured.

<50% compressive strength>
Using the same tester, the strength (kPa) when compressed by 50% with respect to the thickness direction was measured at a test speed of 1 mm / min with reference to the original thickness (50 mm) of the test piece.

<Residual strain>
Using the same tester, compress the sample at 50% compression with respect to the original thickness (50mm) at the test speed of 1mm / min. The sample was allowed to stand for 5 minutes, and the thickness (t) of the test piece after standing was measured. The residual strain (%) was calculated based on the following formula.
Residual strain (%) = (50 mm−thickness (t)) / 50 mm × 100

  The methyleneated melamine-formaldehyde initial condensate synthesized in Example 1 had very good storage stability. Moreover, in Example 2 using the said composite after a 1-hour preservation | save, the melamine resin foam which is lightweight, was rich in a softness | flexibility and elasticity, and the internal shape was porous was obtained. On the other hand, the methylol melamine synthesized in Comparative Example 1 was remarkably inferior in storage stability. Moreover, in the comparative example 2 using the methylol melamine after 1 hour preservation | save, since the nonuniform block-like solid substance produced | generated, the foam could not be manufactured.

Claims (6)

  It is obtained by adding a basic catalyst to an aqueous solution containing melamine monomer and formaldehyde and not containing alcohol, followed by heating to cause a primary reaction, and then adding an acidic catalyst and heating to cause a secondary reaction. A method for producing a methyleneated melamine-formaldehyde initial condensate for foams.   The method for producing a methyleneated melamine-formaldehyde initial condensate for foams according to claim 1, wherein a basic catalyst is added so that the pH of the aqueous solution is 8 or more and less than 11, followed by heating to cause a primary reaction.   The method for producing a methyleneated melamine-formaldehyde initial condensate for foams according to claim 1 or 2, wherein the reaction temperature of the primary reaction is 80 ° C or higher and lower than 110 ° C.   4. The methyleneated melamine-formaldehyde initial condensate for foams according to claim 1, wherein an acidic catalyst is added so that the aqueous solution has a pH of 6 or more and less than 8 and heated to cause a secondary reaction. Manufacturing method.   The method for producing a methyleneated melamine-formaldehyde initial condensate for foams according to any one of claims 1 to 4, wherein the reaction temperature of the secondary reaction is 50 ° C or higher and lower than 80 ° C. A methyleneated melamine-formaldehyde initial condensate for foam (A), a foaming agent (B), an emulsifier (C), and a curing agent (D) obtained by the production method according to claim 1. A method for producing a melamine resin foam, characterized by foaming a mixed solution containing.