Melamine resin foam and its manufacturing method

Abstract

To provide a melamine resin foam which is fine because a cell area and a cell lattice width of the foam is small, has high hardness and rich flexibility because of excellent breaking strength and breaking elongation, has smooth tactile because foreign matter feeling and foreign matter sound are reduced, and can be restored to an original size even after cleaning, and a method for producing the same.SOLUTION: A melamine resin foam contains a melamine-formaldehyde reaction precursor (A), a foaming agent (B), a surface active agent (C), and a curing agent (D), wherein the foaming agent (B) is obtained by foaming a mixed solution containing hydrofluorocarbon (b1) and hydrofluoroether (b2).SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a melamine resin foam and a method for producing the same. [Background technology]

[0002] Melamine-formaldehyde reaction precursors are obtained by reacting melamine monomers with formaldehyde in the presence of a catalyst. Porous melamine resin foams can be produced by adding a blowing agent and heating the resulting mixture. These foams are widely used in household cleaning sponges due to their excellent hardness and durability.

[0003] Melamine resin foams have been widely studied. Specifically, a melamine-formaldehyde reaction precursor-based elastic foam and a method for producing the same are known, which involve foaming an aqueous or alcoholic solution or dispersion containing a melamine-formaldehyde reaction precursor, an emulsifier, a blowing agent, a curing agent, and optionally conventional additives, by irradiating it with an ultra-high frequency wave and curing the foam by crosslinking the precondensate (Patent Document 1).

[0004] However, when the elastic foam according to Patent Document 1 is manufactured and used as a cleaner sponge, although it has excellent hardness and durability, it tends to be somewhat lacking in resilience and feel, leaving room for improvement. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Special Publication No. 2-50943 Summary of the Invention [Problem to be solved by the invention]

[0006] The problem to be solved by the present invention is to provide a melamine resin foam, and a method for producing the same, which has a fine texture due to its small cell area and cell lattice width, high hardness and flexibility due to its excellent breaking strength and breaking elongation, a smooth feel due to its suppressed foreign body sensation and foreign body noise, and the ability to restore its original size even after washing. [Means for solving the problem]

[0007] The present invention provides a melamine resin foam comprising a melamine-formaldehyde reaction precursor (A) obtained by reacting a melamine monomer with formaldehyde in the presence of a catalyst, a blowing agent (B), a surfactant (C), and a curing agent (D), wherein the melamine resin foam is produced by foaming a mixed solution containing a hydrofluorocarbon (b1) and a hydrofluoroether (b2) as the blowing agent (B). [Effects of the Invention]

[0008] The melamine resin foam of the present invention has a fine texture due to its small cell area and cell lattice width, excellent breaking strength and breaking elongation, high hardness and flexibility, a smooth feel due to the suppression of foreign body sensation and foreign body noise, and the ability to restore to its original size even after washing. DETAILED DESCRIPTION OF THE INVENTION

[0009] <Melamine-formaldehyde reaction precursor> The present invention uses a melamine-formaldehyde reaction precursor (A). Component (A) is produced by adding a basic catalyst to an aqueous solution containing melamine monomer and formaldehyde, followed by heating to add formaldehyde to three amino groups present in the melamine monomer. This precursor is also called methylol melamine, and corresponds to the precursor used as the base for the elastic foam described in Patent Document 1.

[0010] Aldehydes other than formaldehyde may be blended within the range that does not impair the effects of the present invention. Examples of other aldehydes include paraformaldehyde, acetaldehyde, propionaldehyde, butyraldehyde, crotonaldehyde, benzaldehyde, acrolein, glyoxal, furfural, salicylaldehyde, and cinnamaldehyde.

[0011] The blending ratio of the melamine monomer to the aldehydes including formaldehyde is preferably a molar ratio of 1:1 to 5, particularly preferably 1:2 to 4. Blending within this range tends to dramatically improve mechanical properties because the molecular structure of the melamine resin becomes a three-dimensional network.

[0012] Examples of the basic catalyst include ammonia and metal hydroxides such as sodium hydroxide, potassium hydroxide, and lithium hydroxide. The basic catalyst is added before the start of the methylolation reaction to adjust the pH of the aqueous solution, and the pH at that time is preferably 8 or more and less than 12, and particularly preferably 8.5 or more and less than 12. When the pH is within this range, the melamine-formaldehyde precondensate tends to be efficiently synthesized.

[0013] The reaction temperature is preferably 80° C. or higher and lower than 110° C., and particularly preferably 85° C. or higher and lower than 105° C. The reaction time is preferably 10 minutes or higher and lower than 3 hours, and particularly preferably 15 minutes or higher and lower than 1 hour and 30 minutes.

[0014] After the above reaction, the melamine-formaldehyde reaction precursor (A) may be subsequently subjected to a methylenation reaction. Specifically, after the synthesis of the methylol melamine, an acidic catalyst is added and the mixture is heated to synthesize a melamine-formaldehyde reaction precursor (A1) having a methylene bond.

[0015] Examples of acidic catalysts include hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, boric acid, paratoluenesulfonic acid, paratoluenesulfonamide, acetic acid, formic acid, and oxalic acid. The acidic catalyst is added after the completion of the methylolation reaction or the etherification reaction and before the initiation of the methylenation reaction to adjust the pH of the aqueous solution, and the pH at this time is preferably 6.0 or more and less than 8.0, and particularly preferably 6.5 or more and less than 7.8. By keeping the pH within this range, the component (A1) can be synthesized efficiently.

[0016] The reaction temperature for the methylenation reaction is preferably 50°C or higher and lower than 90°C, and particularly preferably 55°C or higher and lower than 85°C. The reaction time is preferably 10 minutes or higher and lower than 4 hours, and particularly preferably 15 minutes or higher and lower than 3 hours. As a guide for the completion of the synthesis of the component (A1), a small amount of resin is sampled and gradually cooled, and the reaction can be completed when the temperature at which cloudiness is visually observable (cloud point) is 0 to 10°C.

[0017] After the reaction is complete, a basic catalyst can be added as needed to prevent thickening over time. In this case, the pH is preferably 8.0 or higher but lower than 11.0, and particularly preferably 8.5 or higher but lower than 10.5.

[0018] In the present invention, a melamine resin foam is produced by adding a blowing agent (B), a surfactant (C), and a curing agent (D) to the component (A).

[0019] <Foaming agent> In the present invention, a foaming agent (B) is used. As the component (B), a hydrofluorocarbon (b1) and a hydrofluoroether (b2) are used. The combined use of the components (b1) and (b2) tends to make the melamine resin foam smooth to the touch and improve its recovery.

[0020] As the blowing agent (B), substances other than the above components (b1) and (b2) may be used as long as the effects of the present invention are not impaired. Examples of other blowing agents that can be used include organic and inorganic blowing agents. Examples of organic blowing agents include saturated hydrocarbons having approximately 5 to 18 carbon atoms, azodicarbonamide, dinitrosopentamethylenetetramine, chlorine-based solvents such as methylene chloride and chloroform, and fluorine-based solvents other than (b1) and (b2). Examples of inorganic blowing agents include sodium bicarbonate and ammonium carbonate.

[0021] The blending ratio of the (B) component, converted to the active ingredient, is preferably 0.1 to 100 parts by weight, more preferably 0.5 to 50 parts by weight, and particularly preferably 1 to 30 parts by weight, per 100 parts by weight of the (A) component. Blending within this range tends to enable efficient production of foams with excellent flexibility and elasticity.

[0022] <Surfactant> In the present invention, a surfactant is used. By using the component (C), a uniform solution can be obtained when the components (A) to (D) are mixed. Known components (C) include anionic, cationic, or amphoteric surfactants, as well as nonionic surfactants. Among these, the use of an anionic surfactant is preferred in the present invention. Alternatively, a nonionic surfactant may be mixed with an anionic surfactant.

[0023] Anionic surfactants include carboxylate types such as commercially available soaps and polyoxyethylene alkyl ether carboxylates, sulfonate types such as linear alkylbenzene sulfonates (LAS) and branched alkylbenzene sulfonates (ABS), sulfosuccinate types such as dialkyl sulfosuccinates, sulfate ester types such as alkyl sulfate esters (AS) and polyoxyethylene alkyl ether sulfate esters (AES), as well as phosphate ester types and amino acid types.

[0024] The blending ratio of the (C) component, converted to the active ingredient, is preferably 0.1 to 50 parts by weight, more preferably 0.3 to 30 parts by weight, and particularly preferably 0.5 to 20 parts by weight, per 100 parts by weight of the (A) component. Blending within this range reduces the cell area of ​​the foam, resulting in a finer cell structure and a uniform porous structure, which tends to suppress deviation in cell shape.

[0025] <Curing agent> In the present invention, a curing agent (D) is used. By blending the component (D), the curing reaction of the component (A) after synthesis can be accelerated.

[0026] It is preferable to use an acidic aqueous solution as the component (D). Examples of acidic aqueous solutions include hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, boric acid, acetic acid, formic acid, and oxalic acid. The blending ratio of the component (D), calculated as the active ingredient, is preferably 0.1 to 50 parts by weight, more preferably 0.3 to 30 parts by weight, and particularly preferably 0.5 to 20 parts by weight, per 100 parts by weight of the component (A). Blending within this range tends to enable the component (A) to be cured efficiently.

[0027] A known method can be used to produce the foam, for example, by stirring the components (A) to (D) to obtain a mixed solution, pouring the solution into a suitable mold, and foaming it by heating or irradiating it with microwaves or the like.

[0028] In addition, in the present invention, various additives such as a fluorescent whitening agent, an antioxidant, an ultraviolet absorber, a heat stabilizer, a pigment, a preservative, a salt of an inorganic acid or an organic carboxylic acid, a tackifier, a plasticizer, and a formaldehyde scavenger may be contained.

[0029] EXAMPLES The present invention will be described in more detail below with reference to examples and comparative examples, but these are given as specific examples and are not intended to limit the scope of the present invention. [Example]

[0030] (Synthesis Example 1) 2048 parts by weight of melamine monomer and 3622 parts by weight of formaldehyde (37% aqueous solution) were charged into a three-necked round-bottom flask equipped with a stirrer, reflux condenser, and thermometer, and sodium hydroxide (48% aqueous solution) was added as a basic catalyst to adjust the pH to 9.5. The reaction was carried out at 95°C for 30 minutes, and the methylolation reaction was completed. The pH at the end was 9.0. Thereafter, formic acid (76% aqueous solution) was added so that the pH was adjusted to 7.5, and the reaction was carried out at 75°C for 117 minutes, and the methylenation reaction was completed when the cloud point (5°C) was confirmed. After completion of synthesis, the mixture was allowed to cool naturally. When the temperature had dropped to 60°C, sodium hydroxide (48% aqueous solution) was added again to adjust the pH to 9.0, and excess water was removed until the solid content reached 75%. The mixture was then allowed to cool naturally again to obtain a melamine-formaldehyde reaction precursor (A) having a methylene bond (75% aqueous solution, colorless and transparent, hereinafter referred to as Synthetic Product 1).

[0031] (Synthesis Example 2) 2048 parts by weight of melamine monomer and 3622 parts by weight of formaldehyde (37% aqueous solution) were charged into a three-necked round-bottom flask equipped with a stirrer, reflux condenser, and thermometer, and sodium hydroxide (48% aqueous solution) was added as a basic catalyst to adjust the pH to 12.0. The reaction was carried out at 85°C for 30 minutes, and the methylolation reaction was completed. The pH at the end was 11.0. Thereafter, formic acid (76% aqueous solution) was added so that the pH was adjusted to 7.5, and the reaction was carried out at 75°C for 45 minutes. The methylenation reaction was completed when the cloud point (9°C) was confirmed. After completion of synthesis, the mixture was allowed to cool naturally. When the temperature had dropped to 60°C, sodium hydroxide (48% aqueous solution) was added again to adjust the pH to 9.0, and excess water was removed until the solid content reached 75%. The mixture was then allowed to cool naturally again to obtain a melamine-formaldehyde reaction precursor (A) having a methylene bond (75% aqueous solution, colorless and transparent, hereinafter referred to as Synthetic Product 2).

[0032] Then, using the synthesized product obtained in the above synthesis example, a melamine resin foam was produced by the following steps.

[0033] Example 1 As component (A), 100 parts by weight of compound 1 (75% aqueous solution), The (B) component contains 2.7 parts by weight of hydrofluorocarbon CF3(CF2)5H (boiling point 71°C, surface tension 13.4 mN / m, hereinafter referred to as HFC-1) as component (b1) and hydrofluoroether (CF3)3CFCH2OCFH as component (b2). 2.7 parts by weight of HFE-2 (boiling point 76°C, surface tension 13.6 mN / m), 4.5 parts by weight of n-pentane and 1.1 parts by weight of n-hexane as other blowing agents, 2.4 parts by weight of sodium dodecylbenzenesulfonate (50% aqueous solution) as component (C), 2.1 parts by weight of formic acid (88% aqueous solution) as component (D), and 0.002 parts by weight of fluorescent brightener 4-(2-benzoxazolyl)-4'-(5-methyl-2-benzoxazolyl)stilbene and 1.7 parts of sodium formate as other components were added to a disc turbine mixer and stirred at 3000 rpm for 1 minute to obtain a mixed solution.

[0034] The resulting mixed solution was poured into a polyethylene container and foamed by irradiating it with microwaves at 1.32 kW for 300 seconds using a microwave irradiator (product name: YMD-12, frequency: 2450 MHz, manufactured by Yamamoto Vinita Co., Ltd.). The mixture was then demolded and further heated at 200°C for 30 minutes to completely cure, yielding the melamine resin foam of Example 1.

[0035] (Other Examples) A melamine resin foam was obtained in the same manner as in Example 1 using the formulation shown in Table 1. The following products were used. CF3(CF2)5CH2CH3 (boiling point 114°C, surface tension 15.5mN / m, hereafter referred to as HFC-2) C4H9OCH3 (boiling point 61°C, surface tension 13.6mN / m, hereafter referred to as HFE-1)

[0036] [Table 1]

[0037] The melamine resin foams obtained in the above examples were cut out from the inside of the foam, excluding the surface of the foam, to prepare test pieces, and the physical properties were evaluated. The results are shown in Table 2.

[0038] <Cell area> Using a microscope (product name: VHX-700F, manufactured by Keyence Corporation), each test piece was observed at 300x magnification, and five specimen cells were randomly selected per field of view, resulting in a total of six fields of view, with images of a total of 30 specimen cells being output. The area of ​​each specimen was then measured, and the average value was calculated as the cell area (μm 2 ) was decided.

[0039] <Cell grid width> Using a microscope (product name: VHX-700F, manufactured by Keyence Corporation), each test piece was observed at 700x magnification, and five specimen cells were randomly selected per field of view, resulting in a total of six visual fields, with images of a total of 30 specimen cells being output. The grid width of each specimen was then measured, and the average value was taken as the cell grid width (μm).

[0040] <Breaking strength and elongation> Using a compression testing machine (product name: MCT-2150, manufactured by A&D Co., Ltd.), each test piece (60 mm × 60 mm × 60 mmt) was compressed with a Φ5 cylindrical jig at a test speed of 10 mm / min, and the strength (N) and elongation (mm) at break were measured.

[0041] <Resilience> Each test piece (60mm x 120mm x 30mm) was immersed in tap water and washed a stainless steel sink 100 times. After that, the test piece was left to stand for 30 minutes to check its resilience. If the piece returned to its original size, it was rated as 'Good', and if it did not, it was rated as 'Poor'.

[0042] <Tactile sensation> The feel of each test piece (60 mm x 120 mm x 30 mmt) was checked by touch. If it felt smooth to the touch, it was rated as ◯, and if there was a foreign body sensation or sound, it was rated as ×.

[0043] [Table 2]

Claims

1. A melamine resin foam comprising a melamine-formaldehyde reaction precursor (A), a blowing agent (B), a surfactant (C), and a curing agent (D), the foam being obtained by foaming a mixed solution containing a hydrofluorocarbon (b1) and a hydrofluoroether (b2) as the blowing agent (B).

2. 2. The melamine resin foam according to claim 1, wherein the melamine-formaldehyde reaction precursor (A) is a melamine-formaldehyde reaction precursor (A1) having a methylene bond.

3. 3. The melamine resin foam according to claim 1, wherein the mixed solution contains a fluorescent whitening agent.

4. A method for producing a melamine resin foam, comprising: a melamine-formaldehyde reaction precursor (A); a blowing agent (B); a surfactant (C); and a curing agent (D), wherein the foaming agent (B) is a mixed solution containing a hydrofluorocarbon (b1) and a hydrofluoroether (b2); and wherein the melamine-formaldehyde reaction precursor (A) is obtained by adding a basic catalyst to an aqueous solution containing a melamine monomer and formaldehyde, heating the mixture to cause a reaction, and then adding an acidic catalyst and heating the mixture to cause a reaction.

Images