A pad printing ink for injection molded parts and its preparation method

Abstract

The present application relates to a pad printing ink for injection molded parts and a preparation method thereof. It includes a bottom ink and a top ink. When pad printing, the bottom ink is used to pad print on the surface of the injection molded part, and the top ink is used to pad print on the surface after the bottom ink is cured. The bottom ink comprises the following raw materials in parts by weight: 8-15 parts of epoxy resin, 25-35 parts of polyether diol, 15-25 parts of toluene diisocyanate, 0.5-1.5 parts of chain extender, 5-8 parts of silica white, 0.5-1.5 parts of neutralizer, 0.2-0.5 parts of defoamer, and 20-30 parts of water; the top ink comprises the following raw materials in parts by weight: 40-50 parts of wear-resistant and water-resistant slurry, 35-45 parts of waterborne polyurethane resin, 0.2-0.8 parts of defoamer, and 15-25 parts of water; the ink of the present application is used for the pad printing pattern formed on the injection molded part, which has good wear resistance, high temperature resistance and water resistance.

Description

Technical Field

[0001] This application relates to the technical field of inks, and more specifically, it relates to a pad printing ink for injection molded parts and a preparation method thereof. Background Art

[0002] Injection molded parts refer to various injection molded products produced by an injection molding machine, including various packages, parts, etc. The mobile phone shell is a common injection molded part. Common injection molded parts are not hard enough, have a monotonous appearance color, a single tactile texture, and surface defects, and cannot meet the requirements of the plastic product application field for variable colors, high hardness, wear resistance, delicate texture, and other performance requirements. Pad printing, which can print text, graphics, and images on the surface of the object to be printed, is now becoming an important special printing. The process is very simple. It uses a steel (or copper, thermoplastic) intaglio plate, and a curved pad printing head made of silicone rubber material to dip the ink on the intaglio plate onto the surface of the pad printing head, and then press it on the surface of the object to be pad printed to print text, patterns, etc. Then, the object printed with ink is sent for heat curing or light curing, and the ink is cured to complete the pad printing. However, at present, after the ink is pad printed on the injection molded part, there is still a problem that the printed pattern is easily worn, affecting the beauty of the pattern on the injection molded part. Summary of the Invention

[0003] In order to reduce the easy wear of the ink after pad printing, this application provides a pad printing ink for injection molded parts and a preparation method thereof.

[0004] A pad printing ink for injection molded parts and a preparation method thereof provided by this application adopt the following technical solutions:

[0005] In the first aspect, this application provides a pad printing ink for injection molded parts, adopting the following technical solutions:

[0006] A pad printing ink for injection molded parts includes a bottom layer ink and a surface layer ink. When pad printing, the bottom layer ink is used to pad print on the surface of the injection molded part, and the surface layer ink is used to pad print on the surface after the bottom layer ink is cured. The bottom layer ink includes the following raw materials in parts by weight:

[0007] Epoxy resin: 8 - 15 parts

[0008] Polyether diol: 25 - 35 parts

[0009] Toluene diisocyanate: 15 - 25 parts

[0010] Chain extender: 0.5 - 1.5 parts

[0011] Fumed silica: 5 - 8 parts

[0012] Neutralizer: 0.5 - 1.5 parts

[0013] Defoamer: 0.2 - 0.5 parts

[0014] Water: 20 - 30 parts

[0015] The surface layer ink comprises the following raw materials in parts by weight:

[0016] Abrasion - resistant and water - resistant slurry: 40 - 50 parts

[0017] Water - borne polyurethane resin: 35 - 45 parts

[0018] Defoamer: 0.2 - 0.8 part

[0019] Water: 15 - 25 parts

[0020] Water - borne polyurethane has excellent adhesiveness and flexibility, but poor water resistance and high - temperature resistance, while epoxy resin has better heat resistance and water resistance. Therefore, the bottom layer ink of this application uses toluene diisocyanate and polyether polyol to synthesize a polyurethane base material, and grafts epoxy resin with polyurethane molecular chains, so that the obtained bottom layer ink has better heat resistance and water resistance. And adding a chain extender can expand the molecular chain and form a "bridge" between two polymer chains, significantly increasing the molecular weight of the polymer and improving the viscosity of the system. Thus, the obtained bottom layer ink has better adhesiveness. The chain extender is one or more of 1,4 - butanediol, 1,6 - hexanediol or ethylenediamine.

[0021] In addition, the neutralizer is preferably triethylamine, which has the function of neutralizing the bottom layer ink. The silica is fumed silica, which has excellent stability, reinforcing property, thickening property and thixotropy, improving the adhesiveness of the bottom layer ink. The defoamer reduces the generation of foam in the production or use of the bottom layer ink, which affects the quality or pad printing effect of the bottom layer ink.

[0022] In the surface layer ink, by adding the abrasion - resistant and water - resistant slurry, it has good abrasion resistance and water resistance, so that the surface layer ink has good abrasion resistance and water resistance. When the surface layer ink is pad - printed, the obtained pad - printed pattern has good abrasion resistance and water resistance, reducing the possibility of the pad - printed pattern on the injection - molded part falling off. And using water - borne polyurethane resin can adhere to the surface of the cured bottom layer ink, so that the surface layer ink stably adheres to the surface of the cured bottom layer ink, forming a pad - printed pattern with good stability, and the pad - printed pattern has abrasion resistance. Water plays a diluting role, facilitating the pad - printing of the surface layer ink. Adding a defoamer has a good defoaming effect, reducing the generation of a large amount of foam in the pad - printing or production of the bottom layer ink, which affects the quality of the surface layer ink.

[0023] Furthermore, when this ink is used for pad - printing injection - molded parts, first pad - print the bottom layer ink on the surface of the injection - molded part, then dry it to a humidity of 55 - 65%, obtaining a bottom - surface pad - printed pattern, and then pad - print the surface layer ink on the bottom - surface pad - printed pattern to form a complete pad - printed pattern on the injection - molded part.

[0024] The ink of this application is used for pad printing in combination with the bottom ink and the surface ink, so as to form a pad-printed pattern with good wear resistance, water resistance and high temperature resistance on the surface of the injection molded part.

[0025] Preferably, the wear-resistant and water-resistant slurry is prepared from the following raw materials in parts by weight:

[0026] Modifier: 1 - 3 parts

[0027] Acrylic acid: 15 - 18 parts

[0028] Methyl methacrylate: 5 - 8 parts

[0029] Ethyl acrylate: 3 - 5 parts

[0030] Benzoyl peroxide: 0.3 - 0.5 parts

[0031] Water: 55 - 80 parts

[0032] Emulsifier: 0.5 - 1 part

[0033] Wear-resistant filler: 5 - 10.

[0034] Generally, acrylic resin has a wide range of applications in the fields of adhesives, coatings, etc., and has the advantages of low cost, environmental protection, strong adhesion, long weather resistance, good film-forming property, etc. However, conventional waterborne acrylate resins have defects such as heat resistance.

[0035] Therefore, in the above solution, acrylic acid, methyl methacrylate and ethyl acrylate are used as acrylic resin synthesis monomers, benzoyl peroxide is used as an initiator, and a modifier is added in the monomer polymerization reaction, so that it has good adhesion, water resistance, temperature resistance and alkali resistance; the modifier is composed of γ-aminopropyltriethoxysilane and 3-glycidoxypropyltriethoxysilane in a weight ratio of 1 - 9:1; among them, γ-aminopropyltriethoxysilane contains two different active groups, amino group and ethoxy group, which are used to couple organic polymers and inorganic fillers, enhance their adhesion, and improve the mechanical, water resistance, anti-aging and other properties of the product; 3-glycidoxypropyltriethoxysilane can effectively improve the physical properties and water resistance of waterborne coatings and waterborne adhesive systems, and at the same time ensure a stable storage effect without yellowing. When used as a crosslinking agent or adhesion promoter, it improves water resistance and increases the dry and wet adhesion. Furthermore, γ-aminopropyltriethoxysilane and 3-glycidoxypropyltriethoxysilane are polymerized with the monomers of acrylic resin, and then wear-resistant filler is added for filling, so that the obtained wear-resistant and water-resistant slurry has good water resistance, temperature resistance, etc. Further, the emulsifier is OP-10, and the cloud point of this OP-10 is 60 - 67, and the HLB value is 12 - 13.

[0036] Preferably, the solid content of the aqueous polyurethane resin is 44-46%.

[0037] The surface layer ink obtained by using the aqueous polyurethane resin within the above solid content range can adhere well to the surface after the bottom layer ink is cured; in addition, the aqueous polyurethane resin is an anionic polyurethane with a density of 1.01-1.02 g / cm 3 .

[0038] Preferably, the wear-resistant and water-resistant slurry is obtained by the following preparation method:

[0039] Step 1: Weigh 5-8 parts of methyl methacrylate and 3-5 parts of ethyl acrylate by weight, mix them evenly to obtain a mixed liquid A for standby; hydrolyze 1-3 parts of the modifier in 5-8 parts of water for 25-35 minutes to obtain a hydrolyzed modifier for standby;

[0040] Step 2: Weigh 15-18 parts of acrylic acid, 55-80 parts of water and 1-3 parts of emulsifier by weight, mix them evenly, heat to 50-60 °C, and dropwise add all the hydrolyzed modifiers obtained in Step 1. The dropping time is 35-45 minutes to obtain a mixed liquid B;

[0041] Step 3: Heat the mixed liquid B obtained in Step 2 to 65-75 °C, add all the mixed liquid A obtained in Step 1 in 2-3 batches. After adding each batch, stir for 20-30 minutes and then add another batch. Keep it at a constant temperature for 1-2 hours, finally add the wear-resistant filler, stir for 15-25 minutes, cool, and adjust the pH to 7.5-8.5 to obtain the wear-resistant and water-resistant slurry.

[0042] The wear-resistant and water-resistant slurry obtained by the above preparation method has good wear resistance, high temperature resistance, heat resistance and water resistance. Therefore, the pad printing pattern obtained by applying it to the surface layer ink has good wear resistance, water resistance, high temperature resistance, etc.

[0043] In Step 3, sodium hydroxide is used to adjust the pH value.

[0044] Preferably, the wear-resistant filler is composed of shell powder, hollow glass microspheres and mica powder in a weight ratio of 3-5:1-2:1.

[0045] By selecting shell powder, hollow glass microspheres and mica powder in combination as the wear-resistant filler, when the wear-resistant filler is applied to the surface layer ink, the possibility of the pad printing pattern being damaged or worn can be reduced.

[0046] Preferably, the hollow glass microspheres are alkali-etched hollow microspheres, the wear-resistant filler is a modified wear-resistant filler, and the wear-resistant filler is prepared by the following method:

[0047] Step A: Weigh 3 - 8 parts of sodium hydroxide, 0.5 - 0.8 parts of sodium hexametaphosphate, and 0.3 - 0.5 parts of sodium lignosulfonate, dissolve them in 80 - 120 parts of water, then add 20 - 30 parts of hollow glass microspheres, heat to 65 - 85 °C, vibrate for 1 - 3 h, filter, dry the filter residue to obtain alkali-etched hollow microspheres;

[0048] Step B: Weigh 2 - 4 parts of methacryloxypropyltrimethoxysilane and dissolve it in water, then add alkali-etched hollow microspheres, mica, and shell powder. The weight ratio of alkali-etched hollow microspheres, mica, and shell powder is 3 - 5:1 - 2:1. Stir for 0.5 - 1 h, filter, dry, grind, and sieve through 100 - 200 meshes to obtain modified wear-resistant filler.

[0049] The modified wear-resistant filler obtained by the above preparation method has good wear resistance when used for surface pad printing.

[0050] Among them, methacryloxypropyltrimethoxysilane is a silane coupling agent, which can play a "bridging" role, improve the compatibility of inorganic fillers in polymers, make alkali-etched hollow microspheres, mica, and shell powder evenly dispersed in the raw material system of wear-resistant and water-resistant slurry. Furthermore, the pad printing pattern obtained after pad printing the surface layer ink has good wear resistance.

[0051] Preferably, the particle size of the white carbon black is 2 - 10 μm.

[0052] Selecting white carbon black with the above particle size has a good filling effect and is easy to suspend. When the bottom layer ink is pad printed, the white carbon black is easy to suspend on the surface of the bottom layer ink. After the surface layer ink is pad printed on the cured surface of the injection molded part, the inorganic group of the silane coupling agent in the surface layer ink tightly binds to the white carbon black, thereby tightly bonding the surface layer ink to the surface of the bottom layer ink after pad printing and curing, making the obtained pad printing pattern not easy to fall off.

[0053] Preferably, the defoaming agent in the bottom layer ink raw material and the defoaming agent in the surface layer ink raw material are both polyoxypropylene glycerol ether or polyoxypropylene polyoxyethylene glycerol ether.

[0054] Selecting polyoxypropylene glycerol ether or polyoxypropylene polyoxyethylene glycerol ether as the defoaming agent has a good defoaming effect.

[0055] Preferably, the neutralizing agent is neutralizing agent BYK - 190, where the acid value is 8 - 12 mg KOH / g, the density is 1.0 - 1.1 g / ml, and the non-volatile content is 38 - 42%.

[0056] The neutralizing agent BYK-190 is branded by Kayin Chemical Industry. The test time for the non-volatile content is 10 minutes and the test temperature is 150 °C. Using the neutralizing agent BYK-190 with the above parameters can have a good dispersion effect, thereby improving the dispersion of silica in the bottom ink. At the same time, it can improve the dispersion of the bottom ink, making it easier for the bottom ink to fill into the polymer.

[0057] Secondly, the present application provides a method for preparing pad printing ink for injection molded parts, adopting the following technical solution: The bottom ink is prepared by the following method: Weigh polyether diol and toluene diisocyanate and mix them evenly, heat to 80 - 85 °C, stir and react for 30 - 40 min, add epoxy resin, stir for 20 - 30 min, cool down to 45 - 50 °C, add a neutralizing agent for neutralization, then add water and stir evenly, then add a chain extender and stir for 10 - 20 min, and finally add an antifoaming agent, a neutralizing agent and silica, and stir evenly to obtain the bottom ink;

[0058] The top layer ink is prepared by the following method: Weigh wear-resistant and water-resistant slurry, waterborne polyurethane resin, water and an antifoaming agent, and stir for 20 - 40 min to obtain the top layer ink.

[0059] The above preparation method has the advantages of simple operation and high production efficiency, and the obtained ink is used for pad printing patterns on injection molded parts, making the obtained patterns not easy to fall off and wear-resistant.

[0060] To sum up, the present application has the following beneficial effects:

[0061] 1. Since the top layer ink obtained by using the wear-resistant and water-resistant slurry in the present application is used for pad printing, the printed patterns have good water resistance and abrasion resistance, and by carrying out a copolymerization reaction with epoxy resin and polyurethane raw materials, the molecular weight of the polymer is increased, so that the obtained bottom ink has good adhesion, water resistance and heat resistance;

[0062] 2. In the present application, it is preferably to polymerize γ-aminopropyltriethoxysilane and 3-glycidoxypropyltriethoxysilane with the monomers of acrylic resin, and then add wear-resistant fillers for filling, so that the obtained wear-resistant and water-resistant slurry has good water resistance, heat resistance, etc., and further makes the prepared top layer ink used for pad printing injection molded parts, and the obtained pad printing patterns have good abrasion resistance, water resistance, high temperature resistance, etc.;

[0063] 3. By selecting shell powder, hollow glass microspheres and mica powder in combination as wear-resistant fillers, when the wear-resistant fillers are applied to the top layer ink, the possibility of the pad printing patterns being damaged or worn can be reduced. Specific Embodiments

[0064] The following further elaborates the present application in detail with preparation examples and examples.

[0065] Preparation Example of Wear-Resistant Filler

[0066] Preparation Example 1

[0067] A wear-resistant filler is prepared by the following method:

[0068] Step A: Weigh 3 Kg of sodium hydroxide, 0.5 Kg of sodium hexametaphosphate, and 0.3 Kg of sodium lignosulfonate, dissolve them in 80 Kg of water, then add 20 Kg of hollow glass microspheres (unmodified hollow glass microspheres), heat to 65 °C, place them in an ultrasonic wave for vibration for 3 h, filter, and put the filter residue into an oven at 100 °C for drying for 2 h to obtain alkali-etched hollow glass microspheres;

[0069] Step B: Weigh 2 Kg of methacryloxypropyltrimethoxysilane and dissolve it in water, then add 9 Kg of alkali-etched hollow glass microspheres, 3 Kg of mica, and 3 Kg of shell powder, stir for 0.5 h, filter, put the filter residue into an oven at 60 °C for drying for 5 h, then put it into a grinding machine for grinding, and sieve through 100 meshes to obtain a modified wear-resistant filler.

[0070] Preparation Examples 2 - 3

[0071] The differences between Preparation Examples 2 - 3 and Preparation Example 1 are as follows: the dosages of raw materials are different and the process parameters are different, as shown in Table 1 specifically;

[0072] Table 1 Dosages of Raw Materials (Kg) and Process Parameters of Preparation Examples 1 - 3

[0073]

[0074] Preparation of Comparative Examples

[0075] Preparation of Comparative Example 1

[0076] The difference between Preparation of Comparative Example 1 and Preparation Example 1 is that the shell powder is replaced with mica powder in equal amount.

[0077] Preparation of Comparative Example 2

[0078] The difference between Preparation of Comparative Example 2 and Preparation Example 1 is that both mica and shell powder are replaced with alkali-etched hollow glass microspheres in equal amount.

[0079] Preparation of Comparative Example 3

[0080] A wear-resistant filler is prepared by the following method:

[0081] Weigh 2 Kg of methacryloxypropyltrimethoxysilane and dissolve it in water, then add 12 Kg of mica and 3 Kg of shell powder, stir for 0.5 h, filter, put the filter residue into an oven at 60 °C for drying for 5 h, then put it into a grinding machine for grinding, and sieve through 100 meshes to obtain a modified wear-resistant filler.

[0082] Preparation Example of Wear-Resistant and Water-Resistant Slurry

[0083] Preparation Example 4

[0084] A wear-resistant and water-resistant slurry is prepared by the following method:

[0085] Step 1: Weigh 5 Kg of methyl methacrylate and 3 Kg of ethyl acrylate, mix them evenly to obtain a mixed liquid A for standby; hydrolyze 0.5 Kg of γ-aminopropyltriethoxysilane and 0.5 Kg of 3-glycidoxypropyltriethoxysilane in 5 Kg of water for 25 minutes to obtain a hydrolyzed modifier for standby;

[0086] Step 2: Weigh 15 Kg of acrylic acid, 55 Kg of water and 1 Kg of OP-10, put them into a stirring reaction kettle, start stirring to make the materials mix evenly, heat to 50 °C, and dropwise add all the hydrolyzed modifiers obtained in Step 1. The dropping time is 35 minutes to obtain a mixed liquid B;

[0087] Step 3: Heat the mixed liquid B obtained in Step 2 to 65 °C, add all the mixed liquid A obtained in Step 1 in 2 batches. After adding each batch, stir for 20 minutes and then add the other batch. Keep the temperature constant for 1 hour, finally add the wear-resistant filler, stir for another 15 minutes, cool to 30 °C, and add sodium hydroxide to adjust the pH to 7.5 to obtain the wear-resistant and water-resistant slurry.

[0088] Preparation Examples 5 - 6

[0089] The differences between Preparation Examples 5 - 6 and Preparation Example 4 are: the dosages of raw materials and process parameters are different, as shown in Table 2 specifically;

[0090] Table 2 Dosages of Raw Materials (Kg) and Process Parameters of Preparation Examples 4 - 6

[0091]

[0092]

[0093] Preparation Example 7

[0094] The difference between Preparation Example 7 and Preparation Example 4 is: the wear-resistant filler is selected as the wear-resistant filler of Comparative Example 1.

[0095] Preparation Example 8

[0096] The difference between Preparation Example 8 and Preparation Example 4 is: the wear-resistant filler is selected as the wear-resistant filler of Comparative Example 2.

[0097] Preparation Example 9

[0098] Preparation Example 9 is different from Preparation Example 4 in that the wear-resistant filler used is the wear-resistant filler of Comparative Preparation Example 3.

[0099] Comparative Preparation Example

[0100] Comparative Preparation Example 4

[0101] Comparative Preparation Example 4 is different from Preparation Example 4 in that methyl methacrylate is replaced with ethyl acrylate in equal amounts.

[0102] Comparative Preparation Example 5

[0103] Comparative Preparation Example 5 is different from Preparation Example 4 in that 3-glycidoxypropyltriethoxysilane is replaced with γ-aminopropyltriethoxysilane in equal amounts.

[0104] Example

[0105] Example 1

[0106] A pad printing ink for injection molded parts, comprising a low-layer slurry and a surface-layer slurry;

[0107] The bottom-layer ink is prepared by the following method: Weigh 25 Kg of polyether diol and 15 Kg of toluene diisocyanate and put them into a reaction kettle. Start heating the reaction kettle to 80 °C, stir and react for 30 min, add 8 Kg of epoxy resin, stir for 20 min, stop heating (but continue stirring). When the temperature drops to 45 °C, add 0.5 Kg of neutralizing agent (triethylamine) for neutralization, then add 20 Kg of water, stir evenly, then add 0.5 Kg of ethylenediamine, stir for another 10 min, and finally add 0.2 Kg of polyoxypropylene glycerol ether and 5 Kg of silica, stir evenly to obtain the bottom-layer ink;

[0108] The surface-layer ink is prepared by the following method: Weigh 40 Kg of wear-resistant and water-resistant slurry, 35 Kg of aqueous polyurethane resin (solid content 44%), 15 Kg of water, and 0.2 Kg of polyoxypropylene polyoxyethylene glycerol ether, stir for 20 min to obtain the surface-layer ink.

[0109] Examples 2-8

[0110] Examples 2-8 are different from Example 1 in that the amounts of raw materials used, the sources of wear-resistant connection slurries, and process parameters are different, as shown in Table 3 specifically;

[0111] Table 3 Process parameters, amounts of raw materials used (Kg), and sources of wear-resistant connections for Examples 1-8

[0112]

[0113] Examples 4-8

[0114] Examples 4 - 8 are different from Example 1 in that the sources of the wear - resistant and water - resistant slurries are different, as shown in Table 4 specifically;

[0115] Table 4 Sources of Wear - Resistant and Water - Resistant Slurries in Examples 1 - 8

[0116] Example Abrasion- and water-resistant slurry Example 1 Preparation Example 4 Example 2 Preparation Example 5 Example 3 Preparation Example 6 Example 4 Preparation Example 7 Example 5 Preparation Example 8 Example 6 Preparation Example 9 Example 7 Preparation of Comparative Example 4 Example 8 Preparation of Comparative Example 5

[0117] Comparative Example

[0118] Comparative Example 1

[0119] Comparative Example 1 is different from Example 1 in that the wear - resistant and water - resistant slurry is replaced with an aqueous polyurethane resin in equal amount.

[0120] Comparative Example 2

[0121] Comparative Example 2 is different from Example 1 in that the epoxy resin is replaced with ethylenediamine in equal amount.

[0122] Performance Detection Test

[0123] Detection Method / Test Method

[0124] Apply the inks obtained from Examples 1 - 8 and Comparative Examples 1 - 2 to injection - molded parts. The specific pad - printing steps are as follows:

[0125] Clean the injection - molded parts (clean with 75% alcohol), then put them into an oven at 45°C for drying for 10 min to obtain pre - treated injection - molded parts. Then print the bottom - layer ink on the surface of the pre - treated injection - molded parts, and then dry the imprints on the surface of the pre - treated injection - molded parts in an oven at 80°C until the humidity is 65%. Then use the top - layer ink to pad - print the imprints on the surface of the pre - treated injection - molded parts, and put them into an oven at 100°C for drying for 20 s to form the pad - printed pattern on the surface of the injection - molded parts.

[0126] Set up blank control groups. The difference between Blank Control Group 1 and the above - mentioned pad - printing method is that only the top - layer ink obtained from Example 1 is used for pad - printing to obtain the pad - printed pattern on the surface of the injection - molded parts; Blank Control Group 2, only the bottom - layer ink obtained from Example 2 is used for pad - printing to obtain the pad - printed pattern on the surface of the injection - molded parts.

[0127] Test Method

[0128] 1. Physical Analysis

[0129] Water resistance: Place the injection - molded parts with pad - printed patterns obtained from Examples 1 - 8, Comparative Examples 1 - 2, and Blank Control Groups 1 - 2 in water at 50°C for 2 h. By rubbing, observe whether the pad - printed patterns on the injection - molded parts fall off, and record the relevant data.

[0130] 2. Chemical Analysis

[0131] The injection molded parts with pad printing patterns obtained from Examples 1 - 8, Comparative Examples 1 - 2, and Blank Control Groups 1 - 2 were subjected to the following tests: alcohol resistance test, wiped back and forth 5 times with alcohol of 90% mass fraction, and observed whether there was fading and the data was recorded; abrasion resistance test, the pad printing pattern on the injection molded part was wiped back and forth with an ink abrasion resistance tester until the bottom was revealed or worn, the wiping pressure was 10 N, the effective length of wiping was 2 cm, the effective width of wiping was 1 cm, the number of wiping tests was recorded, high temperature resistance; placed in an oven at 105 °C for 5 min, observed whether there was color change, and the relevant data was recorded. The specific experimental data is shown in Table 5;

[0132] Table 5 Experimental data of Examples 1 - 8, Comparative Examples 1 - 2, and Blank Control Groups 1 - 2

[0133] Test items Alcohol resistance Friction (number of times) High temperature resistance Water resistance Example 1 Fading 531 No color change Not peeled off Example 2 No fading 563 No color change Not peeled off Example 3 No fading 556 No color change Not peeled off Example 4 No fading 535 No color change Not peeled off Example 5 No fading 516 No color change Not peeled off Example 6 No fading 489 No color change Not peeled off Example 7 No fading 511 No color change Not peeled off Example 8 No fading 503 No color change Not peeled off Comparative Example 1 Slight fading 305 Color change A few peeled off Comparative Example 2 Slight fading 450 Color change Peeled off Blank control group 1 No fading 386 No color change Not peeled off Blank control group 2 No fading 336 No color change Not peeled off

[0134] Combined with Example 1 and Comparative Example 1 and Table 5, it can be seen that when the wear - resistant slurry was not added, the number of friction times decreased by 226 (the number of friction times in Example 1 was 531, and the number of friction times in Comparative Example 1 was 305), indicating that the addition of the wear - resistant slurry made the pad printing pattern obtained by ink pad printing have better wear - resistant effect.

[0135] Combined with Example 1 and Comparative Example 2 and Table 5, it can be seen that when epoxy resin was not added, phenomena such as fading, color change, and peeling occurred; indicating that adding epoxy resin can make the ink have better high - temperature resistance, water resistance, and adhesiveness.

[0136] Combined with Example 1 and Examples 4 - 8 and Table 5, it can be seen that when 3 - glycidoxypropyltriethoxysilane and γ - aminopropyltriethoxysilane were compounded, the wear - resistant and water - resistant slurry obtained had better wear resistance; when methyl methacrylate, ethyl acrylate, and acrylic acid were mixed, the wear - resistant and water - resistant slurry obtained had better wear resistance; when mica, shell powder, and alkali - etched hollow microspheres were used in combination, the effect was better.

[0137] This specific embodiment is only an interpretation of the present application, and it does not limit the present application. After reading this specification, those skilled in the art can make modifications to this embodiment without creative contributions as needed, but as long as it is within the scope of the claims of the present application, it is protected by the patent law.

Claims

1. A pad printing ink for injection molded parts, comprising an underlying ink and a surface ink, characterized in that, When pad printing, the underlying ink is used for pad printing on the surface of the injection molded part, and the surface layer ink is used for pad printing on the surface after the underlying ink is cured. The underlying ink comprises raw materials in the following parts by weight: Epoxy resin: 8 - 15 parts Polyether diol: 25 - 35 parts Toluene diisocyanate: 15 - 25 parts Chain extender: 0.5 - 1.5 parts Fumed silica: 5 - 8 parts Neutralizer: 0.5 - 1.5 parts Defoamer: 0.2 - 0.5 parts Water: 20 - 30 parts; The surface layer ink comprises raw materials in the following parts by weight: Wear-resistant and water-resistant slurry: 40 - 50 parts Waterborne polyurethane resin: 35 - 45 parts Defoamer: 0.2 - 0.8 parts Water: 15 - 25 parts; The wear-resistant and water-resistant slurry is obtained by the following preparation method: Step 1: Weigh 5 - 8 parts of methyl methacrylate and 3 - 5 parts of ethyl acrylate according to parts by weight, mix them evenly to obtain a mixed liquid A for standby; Hydrolyze 1 - 3 parts of the modifier in 5 - 8 parts of water for 25 - 35 min to obtain a hydrolyzed modifier for standby; Step 2: Weigh 15 - 18 parts of acrylic acid, 55 - 80 parts of water and 1 - 3 parts of emulsifier according to parts by weight, mix them evenly, heat to 50 - 60 °C, and dropwise add all the hydrolyzed modifiers obtained in Step 1. The dropping time is 35 - 45 min to obtain a mixed liquid B; Step 3: Heat the mixed liquid B obtained in Step 2 to 65 - 75 °C, add all the mixed liquid A obtained in Step 1 in 2 - 3 batches. After adding each batch, stir for 20 - 30 min and then add another batch. Keep the temperature constant for 1 - 2 h, finally add wear-resistant filler, stir for 15 - 25 min, cool, and adjust the pH to 7.5 - 8.5 to obtain the wear-resistant and water-resistant slurry; The modifier is composed of γ-aminopropyltriethoxysilane and 3-glycidoxypropyltriethoxysilane in a weight ratio of 1 - 9:1; The wear-resistant filler is a modified wear-resistant filler, and the wear-resistant filler is prepared by the following method: Step A: Weigh 3 - 8 parts of sodium hydroxide, 0.5 - 0.8 parts of sodium hexametaphosphate, and 0.3 - 0.5 parts of sodium lignosulfonate, dissolve them in 80 - 120 parts of water, then add 20 - 30 parts of hollow glass microspheres, heat to 65 - 85 °C, vibrate for 1 - 3 h, filter, and dry the filter residue to obtain alkali-etched hollow microspheres; Step B: Weigh 2 - 4 parts of methacryloxypropyltrimethoxysilane and dissolve it in water, then add alkali-etched hollow microspheres, mica, and shell powder. The weight ratio of alkali-etched hollow microspheres, mica, and shell powder is 3 - 5:1 - 2:

1. Stir for 0.5 - 1 h, filter, dry, grind, and sieve through 100 - 200 meshes to obtain the modified wear-resistant filler.

2. The pad printing ink for injection molded parts according to claim 1, wherein: The solid content of the waterborne polyurethane resin is 44 - 46%.

3. A pad printing ink for injection molded parts according to claim 1, characterized in that: The particle size of the fumed silica is 2 - 10 μm.

4. A pad printing ink for injection molded parts according to claim 1, characterized in that: The defoamer in the raw materials of the underlying ink and the defoamer in the raw materials of the surface layer ink are both polyoxypropylene glycerol ether or polyoxypropylene polyoxyethylene glycerol ether.

5. A pad printing ink for injection molded parts according to claim 1, characterized in that: The neutralizer is neutralizer BYK-190. The acid value of neutralizer BYK-190 is 8 - 12 mg KOH / g, the density is 1.0 - 1.1 g / ml, and the non-volatile content is 38 - 42%.

6. A method for preparing a pad printing ink for injection molded parts according to any one of claims 1-5, characterized in that, The bottom layer ink is prepared by the following method: Weigh polyether diol and toluene diisocyanate, mix them evenly, heat to 80 - 85 °C, stir and react for 30 - 40 min, add epoxy resin, stir for 20 - 30 min, cool down to 45 - 50 °C, add a neutralizer for neutralization, then add water and stir evenly, then add a chain extender and stir for 10 - 20 min, and finally add an antifoaming agent, a neutralizer and silica white, stir evenly to obtain the bottom layer ink; The surface layer ink is prepared by the following method: Weigh the wear-resistant and water-resistant slurry, waterborne polyurethane resin, water and an antifoaming agent, stir for 20 - 40 min to obtain the surface layer ink.

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