Resin composite, structure, method for producing resin composite, and method for producing structure

Abstract

A resin composite 10 according to the present invention includes: a coating powder 20 used in an electrostatic coating method or a fluidized immersion coating method; an inorganic alkali 30; and a thermoplastic resin 40. The coating powder 20 includes a thermal film-forming resin 26 and a crosslinking agent, and can be molded by one of the following molding methods: injection molding, blow molding, extrusion molding, and vacuum molding.

Description

Resin composite and structure, and method for manufacturing a resin composite and method for manufacturing a structure

[0001] This application claims priority from Japanese Patent Application No. 2023-164059, filed on September 26, 2023, which is incorporated herein by reference in its entirety.

[0002] The present invention relates to a resin composite and a molded article, as well as a method for producing a resin composite and a method for producing a molded article.

[0003] With growing awareness of reducing environmental impacts and a demand for a shift to environmentally friendly products, powder coatings that do not contain organic solvents, are low-polluting, highly workable, and have a smaller environmental impact are attracting attention in the field of coating compositions. Such powder coatings, which are used in electrostatic coating methods and fluidized bed coating methods, are relatively inexpensive, and furthermore, thermosetting powder coatings are easy to color, have strong adhesion to substrates, and form thermosetting films that are highly rust-resistant, weather-resistant, and durable. Therefore, there is strong demand for them for use in electronic components, office automation equipment, home appliances, building materials, automobile parts, etc.

[0004] The electrostatic coating method is a method in which a voltage is applied between an electrically connected object to be coated and a paint spray device, forming an electrostatic field between the two and charging the powder paint, thereby forming a powder paint film on the object to be coated.The fluidized bed method is a method in which the powder paint is lifted by air or the like, and a powder paint film is formed in this area on the surface of a preheated object to be coated.

[0005] The thermosetting powder coatings used in these coating methods are basically composed of a combination of oligomer or polymer particles with crosslinking points that melt and form a film by heating, and crosslinker particles that are compatible with this polymer. The coating is then fixed to the surface of the object to be coated, where it undergoes a film-forming and curing process. The crosslinking method can be categorized into those that utilize the reaction of a blocked isocyanate with ε-caprolactam and a hydroxyl group, those that form an oxazolidone ring between a blocked isocyanate and a bisphenol A-type epoxy resin with epoxy groups at both ends and then harden it (Non-Patent Document 1), those that crosslink a bisphenol A-type epoxy resin with epoxy groups at both ends with ε-caprolactam (Non-Patent Document 2), those that utilize a bonding reaction between an epoxy group and dicyandiamide (Non-Patent Document 3), those that utilize carboxylic acids at both ends of a polyester and harden it with a multifunctional epoxy compound such as triglycyl isocyanurate (Non-Patent Document 4), and those that utilize an esterification reaction.

[0006] However, epoxy-based materials and ε-caprolactam are known to be environmentally toxic because they react with biological components such as proteins. In recent years, β-hydroxyalkylamide (Patent Document 1) has been developed as a compound with a low environmental impact, and a method of crosslinking this material with a polycarboxylic polyester by a dehydration condensation reaction (commonly known as Primid curing type, Non-Patent Document 2) is becoming mainstream.

[0007] Powder coatings have many advantages, but while powder particles that do not adhere to the substrate during coating can be reused, the particle size gradually decreases due to collisions between particles and the substrate, and when an appropriate coating amount cannot be obtained, the particles are discarded. This amount exceeds 10 to 20 percent of the powder coating material added, which has been a major problem. Furthermore, once the polymer particles and crosslinker particles are mixed together, they are difficult to separate, and there are currently no known ways of using the residue other than curing it and using it for another purpose, as in Patent Document 2.

[0008] On the other hand, general-purpose thermoplastic resins can be molded using a variety of methods, including injection molding, extrusion molding, and vacuum forming, and are used in a wide range of applications, including delivery packaging, product display shelves, and simple structures. If powder coatings could be used for such applications, they would allow for the reuse of materials that would otherwise be discarded. Patent Document 3 describes that thermoplastic resins such as polyethylene, polypropylene, and ABS, as well as leveling agents and pigments, may be added to polyester-based powder coatings. However, the purpose is related to thermosetting films, and not to the creation of composites that can be thermoformed, i.e., the use of powder coatings as an extender for thermoplastic resins. However, when powder coatings are compounded with general-purpose thermoplastic resins such as polyethylene, polypropylene, ABS, and PET, the temperature range during mixing is approximately 180°C to 300°C, which means that the powder coating containing a crosslinking agent cures on its own, separating and solidifying from the thermoplastic resin, making it difficult to produce composites.

[0009] Thermosetting Resins, Vol. 6, No. 2, pp. 87-93 (1985) Network Polymers, Vol. 38, No. 2 (2017) Thermosetting Resins, Vol. 8, No. 3, pp. 141-151 (1987) DNT Coating Technical Report, Vol. 10, pp. 32-37 (2010)

[0010] Special Publication No. 2010-508424 Publication of Patent No. 6564988 Publication of Special Publication No. 62-236870

[0011] The present invention provides a thermoformable thermoplastic resin composite containing a thermosetting powder coating.

[0012] The present invention is characterized by the composite of a thermosetting powder coating material, an inorganic alkali, and a thermoplastic resin.

[0013] More specifically, the resin composite of a first embodiment includes a paint powder used in an electrostatic coating method or a fluidized bed coating method, an inorganic alkali, and a thermoplastic resin, and is thermoformable. The resin composite of a second embodiment is the resin composite of the first embodiment, wherein the paint powder includes a thermal film-forming resin and a crosslinking agent.

[0014] The structure of the first embodiment is configured to include the resin composite of the second embodiment and has a predetermined shape.

[0015] The method for producing a resin composite of the first aspect is the method for producing a resin composite of the first or second aspect, and includes a first step of producing a mixture by mixing a solution obtained by dissolving a water-soluble inorganic alkali in water with a paint powder used in an electrostatic coating method or a fluidized bed coating method, and a second step of mixing a thermoplastic resin with the mixture.The method for producing a resin composite of the second aspect is the method for producing a resin composite of the first or second aspect, and includes a first step of producing a mixture by mixing a solution obtained by dissolving a water-soluble inorganic alkali in water with a paint powder used in an electrostatic coating method or a fluidized bed coating method, a second step of drying the mixture to produce a dried product, and a third step of mixing a thermoplastic resin with the dried product.

[0016] The method for producing a structure of the first aspect includes the steps of producing a resin composite by the method of the first aspect and forming the resin composite produced in the step into a structure having a predetermined shape. The method for producing a structure of the second aspect includes the steps of producing a resin composite by the method of the second aspect and forming the resin composite produced in the step into a structure having a predetermined shape.

[0017] A resin composite of a third aspect contains a thermosetting powder coating and an inorganic alkali and is thermoformable. A resin composite of a fourth aspect is the resin composite of the third aspect, characterized in that the thermosetting powder coating contains a polyester resin having a carboxylic acid. A method for producing a resin composite of the third aspect includes adding an inorganic alkali aqueous solution to the thermosetting powder coating and then compounding it with a thermoplastic resin.

[0018] Furthermore, the resin composite of the fourth aspect comprises a paint powder used in an electrostatic coating method or a fluidized bed coating method, an inorganic alkali, and a thermoplastic resin, wherein the paint powder comprises a thermal film-forming resin and a crosslinking agent, and can be molded by any one of injection molding, blow molding, extrusion molding, and vacuum molding.

[0019] Furthermore, the structure of the second embodiment is configured to include the resin composite of the fourth embodiment and has a predetermined shape.

[0020] Furthermore, a fifth aspect of the method for producing a resin composite is the fourth aspect of the method for producing a resin composite, and includes a first step of producing a mixture by mixing a solution in which a water-soluble inorganic alkali is dissolved in water with a paint powder used in an electrostatic coating method or a fluidized bed coating method, and a second step of mixing a thermoplastic resin with the mixture.

[0021] Furthermore, a sixth aspect of the method for producing a resin composite is the fourth aspect of the method for producing a resin composite, and includes a first step of producing a mixture by mixing a solution in which a water-soluble inorganic alkali is dissolved in water with a paint powder used in an electrostatic coating method or a fluidized bed coating method, a second step of drying the mixture to produce a dried product, and a third step of mixing a thermoplastic resin with the dried product.

[0022] Furthermore, the method for producing a structure of the third aspect includes the steps of producing a resin composite by the method of the fifth aspect, and forming the resin composite produced in the step into a structure having a predetermined shape.

[0023] Furthermore, the method for producing a structure of the fourth aspect includes the steps of producing a resin composite by the method of the sixth aspect, and forming the resin composite produced in the step into a structure having a predetermined shape.

[0024] FIG. 1 is a diagram of a resin composite according to an embodiment of the present invention (hereinafter referred to as the present embodiment); FIG. 2 is a flow diagram of a method for manufacturing a resin composite according to the present embodiment; FIG. 3 is another flow diagram of a method for manufacturing a resin composite according to the present embodiment; FIG. 4 is a microscope image (photograph) of powder paint before painting; FIG. 5 is a microscope image (photograph) of powder paint discarded after painting; FIG. 6 is a microscope image (photograph) of a molded resin composite; and FIG. 7 is a photograph of a molded body molded by injection molding.

[0025] The thermoplastic resin composite (resin composite: see reference numeral 10 in the figure) in this embodiment is a composite of a thermosetting powder paint (an example of a paint powder: see reference numeral 20 in the figure) and various thermoplastic resins (see reference numeral 40 in the figure) such as olefin resins such as polyethylene and polypropylene, aliphatic polyesters having properties such as biodegradability, semi-aromatic polyesters such as PET and PBT, aliphatic-aromatic hybrid polyester resins, polystyrene resins, acrylic resins, ABS resins, nylons, and fluororesins.

[0026] The thermosetting powder paint in this embodiment is a paint that does not contain solvents or water. After the polyester is heated to form a film (after the polyester is subjected to a heat-treatment to form a film, resulting in a heat-treated polyester (an example of a thermally film-forming resin, see reference numeral 26 in the figure)), it is thermally cured with a crosslinking agent (see reference numeral 24 in the figure) that is pre-contained in the polyester, ensuring high durability, weather resistance, adhesion, and other properties. Known methods for forming crosslinked structures include blocked isocyanates, epoxy systems, and dehydration condensation of hydroxyl groups and carboxylic acids. However, with the emergence of β-hydroxyalkylamides as crosslinking agents, dehydration condensation systems using these agents are becoming mainstream. In addition to the base resin and crosslinking agent, powder paints may also contain inorganic particles such as silica, alumina, and calcium carbonate, UV inhibitors such as titanium oxide, and even carbon and various colorants. Reference numeral 22 in the figure denotes a pigment contained in the thermosetting powder paint.

[0027] The polyester in this embodiment is a dehydration condensate of an aliphatic diol such as ethylene glycol, 1,4-butanediol, 1,3-propanediol, 1,6-hexanediol, or neopentyl glycol with a polycarboxylic acid compound such as phthalic acid, isophthalic acid, terephthalic acid, phthalic anhydride, 1,4-cyclohexanedicarboxylic acid, adipic acid, sebacic acid, or dodecanedioic acid, and the melting point, crosslink density, and the like are controlled depending on the structure, molecular weight, and number of residual carboxylic acid groups of the selected compound.

[0028] The inorganic alkali (see reference numeral 30 in the figure) used in this embodiment must be water-soluble or hygroscopic, and hydroxides of lithium, sodium, potassium, calcium, etc., or carbonates or formates of lithium, sodium, or potassium are preferred. From the standpoint of storage and handling, sodium hydroxide and carbonates such as sodium bicarbonate and sodium carbonate are more preferred compounds. Inorganic alkalis not only inhibit the dehydration condensation reaction between hydroxyl groups and carboxylic acids, but also dissociate ester bonds in the presence of water or water vapor at high temperatures, thereby decomposing the polymer matrix. On the other hand, organic alkali compounds, such as amines, are alkalis, but they react with carboxylic acids, and in the case of polyvalent amines, they form amide bonds, which are more stable than ester bonds, and therefore are not preferred compounds for the present invention.

[0029] The inorganic alkali is added in the form of a powder or an aqueous solution. As mentioned above, water is essential for inhibiting the curing of powder coatings. Therefore, when using the inorganic alkali in powder form, it is preferable to add a small amount of water or use it in a humidified state. The amount of water added is 0.1 to 200 parts by mass, more preferably 0.2 to 40 parts by mass, per 100 parts by mass of inorganic alkali. This method involves kneading the powder coating and inorganic alkali using a small amount of water without producing excess water. Since powder coatings are hydrophobic, a surfactant or a material with high water retention, such as fine cellulose, methyl cellulose, or sodium salt of carboxymethyl cellulose, may be added during kneading.

[0030] When added in the form of an aqueous solution, the concentration is preferably 0.01 to 30 parts by mass per 100 parts by mass of water, and the amount added is preferably 1 to 500 parts by mass per 100 parts by mass of powder coating; if the inorganic alkali concentration is too low, it is difficult to obtain the desired effect, and if the concentration is too high, workability is impaired, so a concentration of 0.1 to 10 parts by mass is more preferred; if the amount added is too high, excess water increases the fluidity and makes handling difficult, so an added amount of 5 to 50 parts by mass is even more preferred. Since powder coatings are hydrophobic, various activators such as sodium salt of dodecylbenzenesulfonic acid may be added to improve wettability.

[0031] The powder coating mixture (an example of a mixture) to which inorganic alkali has been added is thoroughly kneaded and stirred using a powder kneader or mixer, and then kneaded with a thermoplastic resin in a resin kneader to form a thermoplastic resin composite (see Figure 2). When inorganic alkali is used in powder form, a thorough kneading process is required, so using an aqueous solution is more workable as long as care is taken to prevent excess water. However, if the inorganic alkali concentration is reduced during the process, the mixture may be heated and dried to remove excess water, although this increases the number of manufacturing steps (see Figure 3).

[0032] Thermoforming in this embodiment refers to a method of molding the resin composite 10 produced by the above-described manufacturing method into a molded body having a predetermined shape (see, for example, reference numeral 50 in FIG. 7 ). This is a molding method using a general-purpose thermoplastic resin, such as injection molding, blow molding, extrusion molding, or vacuum molding. Particularly useful molding methods for reuse are injection molding and extrusion molding, which can be processed into trays, panels, tables, chairs, and trolley beds for transportation or display, which can then be crushed and reused. A molded body is an example of a structure having a predetermined shape. In the above description, the resin composite 10 is molded into a molded body having a predetermined shape. However, structures comprising the resin composite 10 may also be manufactured using processing methods other than molding (such as bonding, fusing, cutting, or other processing methods). Shapes of trays, panels, tables, chairs, and trolley beds for transportation or display are examples of predetermined shapes.

[0033] Preliminary experiment A commercially available powder paint, Vilusia (registered trademark) PL7000 (a powder paint in which polyester is cured with β-hydroxyalkylamide) manufactured by Nippon Paint Industrial Coatings Co., Ltd., was used as powder paint 1, and a microscope VHX-2000 manufactured by Keyence Corporation was used to observe the particle state before and after electrostatic coating. The state before electrostatic coating is shown in Figure 4, and the state after electrostatic coating is shown in Figure 5.

[0034] Furthermore, when the particle size was measured using a dry particle size analyzer PSA1190L / D manufactured by Antpearl, the volume average particle size was found to have decreased from 33 μm before coating to 22 μm after coating, and similar to the results of observation under a microscope, a tendency for the particle size to decrease was observed. The powder coating after coating is designated as Powder Coating 2.

[0035] The thermoplastic resins used in the examples are as follows: Polypropylene: Novatec PP BC-06C manufactured by Japan Polypropylene Corporation ABS: GR-2000 manufactured by Denka Co., Ltd.

[0036] Example 1: 100 parts by mass of powder coating 2 was taken out, to which 1 part by mass of sodium carbonate powder, 15 parts by mass of water, and 1 part by mass of fine cellulose were added, and the mixture was thoroughly kneaded in a powder kneader. 20 parts by mass of this kneaded mixture and 80 parts by mass of polypropylene were kneaded in a resin kneader, and composite 1 was taken out in good condition. This composite 1 was then molded into a plate using an injection molding machine.

[0037] Example 2: 100 parts by mass of powder coating material 2 was taken out, and 25 parts by mass of an aqueous sodium carbonate solution adjusted to a concentration of 2% by mass and 4 parts by mass of an aqueous sodium dodecylbenzenesulfonate (abbreviated as DBS) solution with a concentration of 2% by mass were added and stirred. 20 parts by mass of this stirred mixture and 80 parts by mass of polypropylene were kneaded in a resin kneader, and composite 2 could be taken out in good condition. This composite 2 could be molded into a plate using an injection molding machine.

[0038] Example 3: 100 parts by mass of powder coating material 2 was taken out, and 80 parts by mass of a sodium carbonate aqueous solution adjusted to a concentration of 1% by mass and 4 parts by mass of DBS with a concentration of 2% by mass were added and stirred. The stirred product was dried at 130°C for 2 hours. 20 parts of the dried product and 80 parts of ABS were kneaded in a resin kneader, and composite 3 was obtained in good condition. Furthermore, composite 3 was molded into a plate using an injection molding machine.

[0039] Example 4: 100 parts by mass of powder coating material 1 was taken out, and 25 parts by mass of a sodium carbonate aqueous solution adjusted to a concentration of 2% by mass and 4 parts by mass of a DBS aqueous solution with a concentration of 2% by mass were added and stirred. 20 parts by mass of this mixture and 80 parts by mass of polypropylene were kneaded in a resin kneader, and composite 4 was taken out in good condition. This composite 4 was then molded into a plate using an injection molding machine.

[0040] Example 5: 100 parts by mass of powder coating 2 was taken out, and 25 parts by mass of a sodium carbonate aqueous solution adjusted to a concentration of 2% by mass and 4 parts by mass of a DBS aqueous solution were added and stirred. 50 parts by mass of this stirred mixture and 50 parts by mass of polypropylene were kneaded in a resin kneader, and composite 5 was extracted in good condition. Composite 5 was molded into a plate-like body using this injection molding machine. Furthermore, a thin piece was taken out of this molded body, and its surface was observed using a VHX-2000 microscope. Figure 6 shows an image obtained as a result of this observation. As shown in this figure, a broken-shaped composite and spherical polyester were observed after kneading.

[0041] Example 6 Electrostatically coated powder of Bilyusia PL1000 (a powder coating in which bisphenol A epoxy resin is cured with blocked isocyanate) manufactured by Nippon Paint Industrial Coatings Co., Ltd. was designated as powder coating 3. 100 parts by mass of this was taken out, and 25 parts by mass of a 2% by mass aqueous sodium hydroxide solution and 4 parts by mass of a 2% by mass DBS solution were added and stirred. 15 parts of this mixture was then kneaded with 85 parts of polypropylene in a resin kneader to obtain composite 6. Composite 6 could be molded into a plate using an injection molding machine. Comparative Example

[0042] (Comparative Example 1) (When powder coating was directly mixed with polypropylene (1)) When 20 parts by mass of powder coating 1 and 80 parts by mass of polypropylene were mixed in a resin mixer, a solidified material separated and precipitated, and the composite could not be extracted.

[0043] (Comparative Example 2) (When powder coating was directly mixed with polypropylene (2)) When 20 parts by mass of powder coating 2 and 80 parts by mass of polypropylene were mixed in a resin mixer, a solidified material separated and precipitated, and the composite could not be extracted.

[0044] (Comparative Example 3) (When powder coating was directly mixed with polypropylene (3)) When 20 parts by mass of powder coating 3 and 80 parts by mass of polypropylene were mixed in a resin mixer, a solidified material separated and precipitated, and the composite could not be extracted.

[0045] (Comparative Example 4) (When water was added (1)) 100 parts by mass of powder coating material 1 was taken out, 25 parts by mass of water, and 4 parts of a 2% by mass DBS aqueous solution were added, and the mixture was stirred. When 20 parts of this stirred mixture and 80 parts of polypropylene were kneaded in a resin kneader, a solidified product was precipitated, and it was not possible to extract a composite.

[0046] (Comparative Example 5) (When water was added (2)) 100 parts by mass of powder coating material 2 was taken out, and 25 parts by mass of water and 4 parts of a 2% by mass DBS aqueous solution were added and stirred. When 20 parts of this stirred mixture and 80 parts of polypropylene were kneaded in a resin kneader, a solidified product was precipitated and it was not possible to extract a composite.

[0047] (Comparative Example 6) (When water was added (3)) 100 parts by mass of powder coating material 3 was taken out, and 25 parts by mass of water and 4 parts of a 2% by mass DBS aqueous solution were added and stirred. When 20 parts of this stirred mixture and 80 parts of polypropylene were kneaded in a resin kneader, a solidified product was precipitated and it was not possible to extract a composite.

[0048] (Comparative Example 7) (When ethylenediamine was used as the organic alkali (1)) 100 parts by mass of powder coating material 1 was taken out, and 25 parts by mass of ethylenediamine adjusted to a concentration of 4% by mass and 4 parts by mass of a 2% by mass aqueous DBS solution were added and stirred. When 20 parts by mass of this stirred product and 80 parts by mass of polypropylene were kneaded in a resin kneader, a solidified product was precipitated and it was not possible to extract a composite.

[0049] (Comparative Example 8) (When ethylenediamine was used as the organic alkali (2)) 100 parts by mass of powder coating material 2 was taken out, and 25 parts by mass of ethylenediamine adjusted to a concentration of 4% by mass and 4 parts by mass of a 2% by mass aqueous DBS solution were added and stirred. When 20 parts by mass of this stirred product and 80 parts by mass of polypropylene were kneaded in a resin kneader, a solidified product was precipitated and it was not possible to extract a composite.

[0050] (Comparative Example 9) (When ethylenediamine was used as the organic alkali (3)) 100 parts by mass of powder coating material 3 was taken out, and 25 parts by mass of ethylenediamine adjusted to a concentration of 4% by mass and 4 parts by mass of a 2% by mass aqueous DBS solution were added and stirred. When 20 parts by mass of this stirred product and 80 parts by mass of polypropylene were kneaded in a resin kneader, a solidified product was precipitated and it was not possible to extract a composite.

[0051] (Discussion) In the Examples, an inorganic alkali was added to the powder coating, and in all cases, a composite and a molded article using the same were obtained. On the other hand, Comparative Examples 1 to 3 are the results of directly compounding the powder coating and thermoplastic resin, Comparative Examples 4 to 6 are the results of adding only water during kneading, and Comparative Examples 7 to 9 are the results of using an organic alkali, but in all cases, a composite could not be obtained after kneading, demonstrating that the combined use of an inorganic alkali is extremely effective in achieving the object of the present invention, that is, a method of obtaining a thermoplastic resin composite containing a powder coating.

[0052] REFERENCE SIGNS LIST 10 Resin composite 20 Paint powder 22 Pigment 24 Additive 26 Thermal film-forming resin 30 Inorganic alkali 40 Thermoplastic resin 50 Molded body

Claims

1. A resin composite comprising: a paint powder for use in an electrostatic coating method or a fluidized bed coating method; an inorganic alkali; and a thermoplastic resin, wherein the paint powder contains a thermally film-forming resin and a crosslinking agent, and the resin composite can be molded by any one of an injection molding method, a blow molding method, an extrusion molding method, and a vacuum molding method.

2. A structure comprising the resin composite according to claim 1 and having a specified shape.

3. A method for producing a resin composite according to claim 1, comprising: a first step of producing a mixture by mixing a solution in which a water-soluble inorganic alkali is dissolved in water with a paint powder used in an electrostatic coating method or a fluidized bed coating method; and a second step of mixing a thermoplastic resin with the mixture.

4. A method for producing a resin composite according to claim 1, comprising: a first step of producing a mixture by mixing a solution in which a water-soluble inorganic alkali is dissolved in water with a paint powder used in an electrostatic coating method or a fluidized bed coating method; a second step of drying the mixture to produce a dried product; and a third step of mixing a thermoplastic resin with the dried product.

5. A method for producing a structure, comprising: a step of producing a resin composite by the method according to claim 3; and a step of forming the resin composite produced in said step into a structure having a predetermined shape.

6. A method for producing a structure, comprising: a step of producing a resin composite by the method according to claim 4; and a step of forming the resin composite produced in said step into a structure having a predetermined shape.

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