A method for preparing modified melamine resin daylight fluorescent pigment

Abstract

The invention discloses a method for preparing a modified melamine resin daylight fluorescent pigment, and relates to the technical field of fluorescent pigments. The invention introduces polyethylene glycol and urea into a melamine resin for modification, prepares a modified melamine resin as a carrier resin, and then mixes the carrier resin with a fluorescent dye and an auxiliary agent to prepare a modified melamine resin daylight fluorescent pigment. The fluorescent pigment prepared in the present application has better heat resistance, solvent resistance, migration resistance, light resistance, higher softening point and better fluorescence; compared with other melamine resin daylight fluorescent pigments, the formaldehyde content is low and the environment is friendly.

Description

Technical Field

[0001] The invention relates to the technical field of fluorescent pigments, and in particular to a method for preparing a modified melamine resin daylight fluorescent pigment. Background Art

[0002] Daylight fluorescent pigment is a special organic pigment that can emit fluorescence under sunlight or ultraviolet light. The color of the product is very bright and is widely used in the coloring of plastics, paints, inks, candles, and textiles. Daylight fluorescent pigments are composed of carrier resins, fluorescent dyes, and additives. The fluorescent dyes give the pigments a fluorescent effect, while the carrier resins determine the pigments' solvent resistance, migration, heat resistance, and other properties. The more common daylight fluorescent pigments on the market are currently divided into polyesters, polyamides, polyureas, melamines, and styrene-acrylic emulsions according to the carrier resins.

[0003] Polyester, polyamide, and styrene acrylic emulsions can only be used in the field of plastic coloring because of their poor solvent resistance and low resin softening point (<150°C). Daylight fluorescent pigments resistant to common solvents (such as common organic solvents) are made from a p-toluenesulfonamide-formaldehyde-melamine resin system. The resin is cross-linked by adding melamine to make it solvent-resistant. Generally speaking, the greater the amount of melamine added, the better the solvent resistance. However, with the increase of melamine, the viscosity of the resin increases, the dyeing is uneven, and the reaction operation time is greatly shortened, so this method cannot produce daylight fluorescent pigments with high solvent resistance.

[0004] Japan Catalyst Chemical Co., Ltd. has developed an emulsion curing method using benzoguanamine-formaldehyde resin as a carrier. First, a low-condensation benzoguanamine-formaldehyde resin is synthesized, then high-shear emulsification is performed, and finally curing is performed under acidic conditions to obtain a 1.5-3um microsphere-type solvent-resistant daylight fluorescent pigment. However, there are also the following disadvantages: 1. The free formaldehyde content is high during the production process; 2. There is also a slight bleeding phenomenon when resistant to strong solvents.

[0005] In 1998, Day-Glo Company released solvent-resistant ion polymer fluorescent pigments, which used polyamines, polyanhydrides, metal compounds, and epoxy resins to make organic-inorganic composite particle polymers, and fully cross-linked them using ionic bonds, greatly improving the product's solvent resistance. However, due to the poor water resistance of ionic bonds, it is easy to agglomerate during storage and easily cause color bleeding due to water when used.

[0006] Therefore, in view of the above-mentioned technical problems existing in the benzenesulfonamide-formaldehyde-melamine resin system type daylight fluorescent pigment, a modified melamine resin type daylight fluorescent pigment is invented, and the product has significantly improved heat resistance, solvent resistance, migration resistance, and light resistance, as well as a higher softening point and better fluorescence. Summary of the invention

[0007] The purpose of the present invention is to provide a method for preparing a modified melamine resin daylight fluorescent pigment to solve the following technical problems:

[0008] Existing daylight fluorescent pigments have poor solvent resistance and are prone to color bleeding; they also have poor storage resistance and are prone to agglomeration.

[0009] The purpose of the present invention can be achieved through the following technical solutions:

[0010] A method for preparing a modified melamine resin daylight fluorescent pigment comprises the following steps:

[0011] S1: adding benzoguanamine and paraformaldehyde into a reaction kettle, heating and stirring, adjusting the pH to alkaline, and reacting at the temperature to obtain a mixture A;

[0012] S2: adding polyethylene glycol to mixture A, and reacting at the same temperature to obtain mixture B;

[0013] S3: adding methanol to mixture B, adjusting the pH to acidic, and keeping the temperature to react to obtain mixture C;

[0014] S4: adding urea to the mixture C, heating, maintaining the temperature and stirring to obtain a modified melamine resin;

[0015] S5: adding fluorescent dye and auxiliary agent into modified melamine resin, stirring evenly, discharging, cooling, drying and crushing to obtain modified melamine resin daylight fluorescent pigment.

[0016] As a further embodiment of the present invention, the mass ratio of benzoguanamine: paraformaldehyde: polyethylene glycol: methanol: urea is 90-100: 40-110: 6-10: 40-110: 4-7.

[0017] As a further solution of the present invention: the mass ratio of modified melamine resin: fluorescent dye: auxiliary agent is 100:3-7:1-2.

[0018] As a further solution of the present invention: adjusting the pH to alkaline in S1 is specifically to add a sodium hydroxide aqueous solution with a mass concentration of 10% to adjust the pH to 8.5-9.

[0019] As a further solution of the present invention: adjusting the pH to acidic in S3 is specifically to add a citric acid aqueous solution with a mass concentration of 10% to adjust the pH to 5-5.5.

[0020] As a further solution of the present invention: the heat preservation reaction in S1 is specifically to raise the temperature to 80-90° C. and to keep the temperature for 10-20 minutes.

[0021] As a further solution of the present invention: the heat preservation reaction in S2 is specifically to raise the temperature to 80-90° C. and to keep the temperature for 20-40 minutes.

[0022] As a further solution of the present invention: the heat preservation reaction in S3 is specifically cooling to 40-60° C. and heat preservation reaction for 60-70 minutes.

[0023] As a further solution of the present invention: the heating and heat preservation and stirring in S4 are specifically heating to 75-95° C. and heat preservation and stirring for 20-40 minutes.

[0024] As a further solution of the present invention: the molecular weight of the modified melamine resin is 7000-9000.

[0025] As a further solution of the present invention: the particle size of the modified melamine resin daylight fluorescent pigment is 2-4 um.

[0026] As a further embodiment of the present invention: the fluorescent dye is one or more of Solvent Red 196, Solvent Red 197, Solvent Red 49, Solvent Red 149, Basic Red 1, Basic Red 1:1, Basic Violet 10, Basic Violet 11, Basic Violet 11:1, Basic Yellow 40, Solvent Violet 9, Solvent Yellow 172, and Solvent Yellow 145 mixed in any ratio.

[0027] As a further solution of the present invention: the auxiliary agent is one or more of an antioxidant, an ultraviolet red absorber, a dispersant, and an antistatic agent mixed in any ratio.

[0028] Beneficial effects of the present invention:

[0029] (1) The present invention uses benzoguanamine and paraformaldehyde as raw materials, and the amino groups on the benzoguanamine react with the formaldehyde after the depolymerization of the paraformaldehyde to undergo hydroxylation reaction and then polycondense to prepare the melamine resin. Polyethylene glycol is also introduced into the melamine resin reaction system for modification. Polyethylene glycol is a straight-chain triol that can connect the triazine rings in the melamine resin to lengthen the connecting chain between molecules and remove the remaining methylol groups. The cross-linking degree between the resins is high, and compared with ordinary amino resins, the melamine resin has better heat resistance, solvent resistance, migration resistance, light resistance, higher softening point and better fluorescence.

[0030] (2) The present invention also introduces urea into the melamine resin for modification, which undergoes a cyclization reaction with formaldehyde. The amine groups in the urea react with formaldehyde to generate hydroxymethyl urea. When the addition reaction of benzoguanamine and formaldehyde has reached a certain level, free formaldehyde can react with the amine groups in the urea to generate hydroxymethyl urea, thereby reducing the amount of formaldehyde released and thus greatly reducing the formaldehyde content of the product. DETAILED DESCRIPTION

[0031] The following will be described clearly and completely in conjunction with the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0032] Example 1

[0033] A method for preparing a modified melamine resin comprises the following steps:

[0034] (1) 95 g of benzoguanamine and 43 g of paraformaldehyde were added to a reaction kettle, stirred, heated to 85° C., 10 g of a 10% sodium hydroxide aqueous solution was added, and the mixture was kept at 85° C. for 10 min to obtain a mixture A;

[0035] (2) adding 9 g of polyethylene glycol to mixture A, and reacting at 85° C. for 30 min to obtain mixture B;

[0036] (3) lowering the temperature to 50° C., adding 42 g of methanol to mixture B, adding 62 g of a 10% by mass aqueous solution of citric acid, and reacting at 50° C. for 60 min to obtain mixture C;

[0037] (4) Add 4.5 g of urea to mixture C, raise the temperature to 85° C., and keep the temperature to react for 30 min to obtain a modified melamine resin.

[0038] Example 2

[0039] A method for preparing a modified melamine resin comprises the following steps:

[0040] (1) 96 g of benzoguanamine and 62 g of paraformaldehyde were added to a reaction kettle, stirred, heated to 85° C., 9 g of a 10% sodium hydroxide aqueous solution was added, and the mixture was kept at 85° C. for 10 min to obtain a mixture A;

[0041] (2) adding 6.5 g of polyethylene glycol to mixture A, and reacting at 85° C. for 30 min to obtain mixture B;

[0042] (3) lowering the temperature to 50° C., adding 63 g of methanol to mixture B, adding 62 g of a 10% by mass aqueous solution of citric acid, and reacting at 50° C. for 60 min to obtain mixture C;

[0043] (4) Add 4.2 g of urea to mixture C, raise the temperature to 85° C., and keep the temperature to react for 30 min to obtain a modified melamine resin.

[0044] Example 3

[0045] A method for preparing a modified melamine resin comprises the following steps:

[0046] (1) 96 g of benzoguanamine and 83 g of paraformaldehyde were added to a reaction kettle, stirred, heated to 85° C., 7.5 g of a 10% sodium hydroxide aqueous solution was added, and the mixture was kept at 85° C. for 10 min to obtain a mixture A;

[0047] (2) adding 7.5 g of polyethylene glycol to mixture A, and reacting at 85° C. for 30 min to obtain mixture B;

[0048] (3) lowering the temperature to 50° C., adding 82 g of methanol to mixture B, adding 56 g of a 10% by mass aqueous solution of citric acid, and reacting at 50° C. for 60 min to obtain mixture C;

[0049] (4) Add 5.5 g of urea to mixture C, raise the temperature to 85° C., and keep the temperature to react for 30 min to obtain a modified melamine resin.

[0050] Example 4

[0051] A method for preparing a modified melamine resin comprises the following steps:

[0052] (1) 96 g of benzoguanamine and 106 g of paraformaldehyde were added to a reaction kettle, stirred, heated to 85° C., 6 g of a 10% sodium hydroxide aqueous solution was added, and the mixture was kept at 85° C. for 10 min to obtain a mixture A;

[0053] (2) adding 9.6 g of polyethylene glycol to mixture A, and reacting at 85° C. for 30 min to obtain mixture B;

[0054] (3) lowering the temperature to 50° C., adding 104 g of methanol to mixture B, adding 62 g of a 10% by mass aqueous solution of citric acid, and reacting at 50° C. for 60 min to obtain mixture C;

[0055] (4) Add 6.6 g of urea to mixture C, raise the temperature to 85° C., and keep the temperature to react for 30 min to obtain a modified melamine resin.

[0056] Example 5

[0057] A method for preparing a modified melamine resin daylight fluorescent pigment comprises the following steps:

[0058] 1.8 g of fluorescent dye, 0.7 g of auxiliary agent and 60 g of modified melamine resin prepared in Example 1 were added into a reaction kettle, stirred at high speed, discharged, rapidly cooled, filter pressed and dried; the dried material was coarsely crushed, and further air flow crushed to obtain a modified melamine resin daylight fluorescent pigment.

[0059] Example 6

[0060] Compared with Example 5, only the modified melamine resin prepared in Example 1 added in Example 5 is replaced by the modified melamine resin prepared in Example 2 in equal amount, and the remaining component proportions and preparation methods are consistent with those in Example 5.

[0061] Example 7

[0062] Compared with Example 5, only the modified melamine resin prepared in Example 1 added in Example 5 is replaced by the modified melamine resin prepared in Example 3 in equal amount, and the remaining component proportions and preparation methods are consistent with those in Example 5.

[0063] Example 8

[0064] Compared with Example 5, only the modified melamine resin prepared in Example 1 added in Example 5 is replaced by the modified melamine resin prepared in Example 4 in equal amount, and the remaining component proportions and preparation methods are consistent with those in Example 5.

[0065] Comparative Example 1

[0066] A method for preparing a carrier resin comprises the following steps:

[0067] (1) Add 62 g of melamine, 76 g of paraformaldehyde, and 195 g of p-toluenesulfonamide into a reaction kettle, start stirring, raise the temperature to 110° C., and keep the temperature for reaction for 10 min;

[0068] (2) The temperature was further raised to 130° C., 36 g of a 10% by mass aqueous solution of citric acid was added, and the mixture was reacted for 10 min to obtain a carrier resin.

[0069] Comparative Example 2

[0070] A method for preparing a carrier resin comprises the following steps:

[0071] (1) 95 g of benzoguanamine and 43 g of paraformaldehyde were added to a reaction kettle, stirred, heated to 85° C., 10 g of a 10% sodium hydroxide aqueous solution was added, and the mixture was kept at 85° C. for 10 min to obtain a mixture A;

[0072] (2) lowering the temperature to 50° C., adding 42 g of methanol to mixture B, adding 62 g of a 10% by mass aqueous solution of citric acid, and reacting at 50° C. for 60 min to obtain mixture C;

[0073] (3) Add 4.5 g of urea to mixture C, raise the temperature to 85° C., and keep the temperature to react for 30 min to obtain a carrier resin.

[0074] Comparative Example 3

[0075] A method for preparing a carrier resin comprises the following steps:

[0076] (1) 95 g of benzoguanamine and 43 g of paraformaldehyde were added to a reaction kettle, stirred, heated to 85° C., 10 g of a 10% sodium hydroxide aqueous solution was added, and the mixture was kept at 85° C. for 10 min to obtain a mixture A;

[0077] (2) adding 9 g of polyethylene glycol to mixture A, and reacting at 85° C. for 30 min to obtain mixture B;

[0078] (3) The temperature was lowered to 50° C., 42 g of methanol was added to the mixture B, and 62 g of a 10% by mass aqueous solution of citric acid was added. The mixture was kept at 50° C. for 60 min to obtain a carrier resin.

[0079] Comparative Example 4

[0080] Compared with Example 5, only the modified melamine resin prepared in Example 1 added in Example 5 is replaced by an equal amount of the carrier resin prepared in Comparative Example 1, and the remaining component proportions and preparation methods are consistent with those in Example 5.

[0081] Comparative Example 5

[0082] Compared with Example 5, only the modified melamine resin prepared in Example 1 added in Example 5 is replaced by an equal amount of the carrier resin prepared in Comparative Example 2, and the remaining component proportions and preparation methods are consistent with those in Example 5.

[0083] Comparative Example 6

[0084] Compared with Example 5, only the modified melamine resin prepared in Example 1 added in Example 5 is replaced by an equal amount of the carrier resin prepared in Comparative Example 3, and the remaining component proportions and preparation methods are consistent with those in Example 5.

[0085] Performance Testing

[0086] (1) Solvent resistance test: 1 g of the pigment prepared in Examples 5-8 and Comparative Examples 4-6 was added to 15 g of solvent and shaken well. After 24 hours, the state of the pigment in the solvent was observed. The test results are shown in Table 1.

[0087] Table 1: Test of solvent resistance of Examples 5-8 and Comparative Examples 4-6

[0088]

[0089] (2) Migration test: Take 0.36g of the pigments prepared in Examples 5-8 and Comparative Examples 4-6, add them to 150g of PVC resin particles, respectively, and make injection molded plates at 170°C, and press the above injection molded plates and blank injection molded plates (without pigment) in a 60°C oven. Paste the colorless transparent plate that has not been used for migration resistance and two colorless transparent plates that have been used for migration resistance side by side on A4 paper, and paste the colorless transparent plate that has not been used for migration resistance in the middle, and the two colorless transparent plates that have been used for migration resistance on both sides. Visually observe the color of the two colorless transparent plates that have been used for migration resistance to judge the migration resistance of the product. If no color is seen on the two colorless transparent plates that have been used for migration resistance, it can be determined that the product has good migration resistance. On the colorimeter, set the colorless transparent sample that has not been used for migration resistance as the benchmark, and measure the color difference of the two colorless transparent samples that have been tested for migration resistance. If the color difference of the two samples is ≤0.5, it can be determined that the product has good migration resistance. The test results are shown in Table 2-3.

[0090] Table 2: Migration performance test of Examples 5-8 and Comparative Examples 4-6

[0091] 1d 3d 7d 15d 30d Example 5 No Color Light Darker Dark Dark Example 6 No Color Light Darker Dark Dark Example 7 No Color No Color Light Light Light Example 8 No Color No Color Light Darker Dark Comparative Example 4 Light Darker Dark Dark Dark Comparative Example 5 No Color Light Darker Dark Dark Comparative Example 6 No Color Light Darker Dark Dark

[0092] Table 3: Color difference data in migration performance test of Examples 5-8 and Comparative Examples 4-6

[0093]

[0094]

[0095] As shown in Table 2-3, through visual observation and instrumental color difference measurement, it can be seen that the pigment prepared in Example 7 has the best migration resistance and can last for more than 30 days.

[0096] (3) Lightfastness test: Weigh 6 g of the pigments prepared in Examples 5-8 and Comparative Examples 4-6 and place them in 50 mL stainless steel cups, add 14 g of transparent ink and stir evenly in a mixer. Place the stirred samples on a white cloth strip and apply evenly with a scraper. The effective coating area is not less than 5 cm × 3 cm. Use the same method to draw out 10 white cloth strip samples.

[0097] The sample cloths were simultaneously exposed in a sun drying area with sufficient sunlight (or in a UV aging box with the temperature set at 40°C). The exposure time was analyzed as follows: 4, 8, 16, 32, 64, and 72 hours. The unexposed sample cloth was used as the standard to test the color difference. The smaller the color difference, the better the light resistance. The test results are shown in Table 4.

[0098] Table 4: Light resistance test data of Examples 5-8 and Comparative Examples 4-6

[0099] 2h 4h 8h 16h 32h 72h Example 5 0.35 0.86 1.21 1.56 2.81 3.62 Example 6 0.28 0.69 0.95 1.29 2.65 4.15 Example 7 0.08 0.15 0.26 0.32 0.47 0.68 Example 8 0.24 0.23 0.45 0.86 1.65 2.59 Comparative Example 4 1.25 2.93 4.65 5.33 6.41 7.25 Comparative Example 5 0.43 1.45 2.21 3.77 5.11 5.99 Comparative Example 6 0.39 1.37 2.08 3.41 4.78 5.67

[0100] It can be seen from Table 4 that the pigment prepared in Example 7 of the present application has the best light resistance effect.

[0101] (4) Tested according to industry standard HG / T5188-2017 “Daylight Fluorescent Pigments”. The test results are shown in Table 5.

[0102] Table 5: Relevant test data of Examples 5-8 and Comparative Examples 4-6

[0103]

[0104]

[0105] Compared with the existing toluenesulfonamide-formaldehyde-melamine resin system fluorescent pigment and the pigment prepared in comparative examples 4-5, the melamine resin daylight fluorescent pigment prepared by the present invention and modified by adding polyethylene glycol and urea has significantly improved solvent resistance, migration resistance, heat resistance and light resistance, high softening point and better fluorescence of the product.

[0106] The above is a detailed description of an embodiment of the present invention, but the content is only a preferred embodiment of the present invention and cannot be considered to limit the scope of implementation of the present invention. All equivalent changes and improvements made within the scope of the present invention should still fall within the scope of the patent coverage of the present invention.

Claims

1. A method for preparing a modified melamine resin daylight fluorescent pigment, characterized in that: The steps include: S1: adding benzoguanamine and paraformaldehyde into a reaction kettle, heating and stirring, adjusting the pH to alkaline, and reacting at the temperature to obtain a mixture A; S2: adding polyethylene glycol to mixture A, and reacting at the same temperature to obtain mixture B; S3: adding methanol to mixture B, adjusting the pH to acidic, and keeping the temperature to react to obtain mixture C; S4: adding urea to the mixture C, heating, maintaining the temperature and stirring to obtain a modified melamine resin; S5: adding fluorescent dye and auxiliary agent into modified melamine resin, stirring evenly, discharging, cooling, drying and crushing to obtain modified melamine resin daylight fluorescent pigment; The mass ratio of benzoguanamine: paraformaldehyde: polyethylene glycol: methanol: urea is 90-100: 40-110: 6-10: 40-110: 4-7; Modified melamine resin: The mass ratio of fluorescent dye: auxiliary agent is 100:3-7:1-2.

2. The method for preparing a modified melamine resin daylight fluorescent pigment according to claim 1, characterized in that: In S1, the pH is adjusted to alkaline by adding a sodium hydroxide aqueous solution with a mass concentration of 10% to adjust the pH to 8.5-9.

3. The method for preparing a modified melamine resin daylight fluorescent pigment according to claim 1, characterized in that: In S3, the pH is adjusted to be acidic by adding a 10% mass concentration of citric acid aqueous solution to adjust the pH to 5-5.

5.

4. The method for preparing a modified melamine resin daylight fluorescent pigment according to claim 1, characterized in that: The heat preservation reaction in S1 is specifically to raise the temperature to 80-90° C. and to keep the temperature for 10-20 minutes.

5. The method for preparing a modified melamine resin daylight fluorescent pigment according to claim 1, characterized in that: The heat preservation reaction in S2 is specifically to raise the temperature to 80-90° C. and keep the temperature for 20-40 minutes.

6. The method for preparing a modified melamine resin daylight fluorescent pigment according to claim 1, characterized in that: The heat preservation reaction in S3 is specifically to cool to 40-60° C. and to keep the temperature for 60-70 minutes.

7. The method for preparing a modified melamine resin daylight fluorescent pigment according to claim 1, characterized in that: The heating and heat preservation and stirring in S4 specifically include heating to 75-95° C. and heat preservation and stirring for 20-40 minutes.

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