Preparation method of yellowing-resistant light-color PVC male mold skin and product of yellowing-resistant light-color PVC male mold skin

Abstract

The invention discloses a preparation method of an anti-yellowing light-color PVC male mold skin and a product thereof, relates to the technical field of artificial leather, and aims to solve the problem that the anti-yellowing performance of the light-color PVC male mold skin is difficult to break through after encountering an auxiliary saturation effect. The modified PVC surface layer is prepared by mixing materials and then carrying out melt extrusion, film casting and cooling molding, the weight ratio of PVC resin powder to a heat-resistant auxiliary agent to an amine-resistant auxiliary agent to a heat-resistant pigment in the raw materials is 100: 0.5 a: 0.5 a: 0.3 a, and a is 2-4; the foaming layer is obtained by blending raw materials, melting, extruding, foaming, forming and cooling, and the modified PVC surface layer and the foaming layer are bonded through a binder; one side, far away from the foaming layer, of the modified PVC surface layer is coated with a coating agent in a roller coating mode, a surface coating is formed after drying, and the yellowing-resistant light-color PVC male mold surface is prepared; the contents of the heat-resistant auxiliary agent, the amine-resistant auxiliary agent and the heat-resistant pigment are increased in the same proportion, the respective saturation effects of the three materials are broken through, and the yellowing resistance of the light-color PVC male mold skin is greatly improved.

Description

Technical Field

[0001] This invention relates to the field of artificial leather technology, specifically to a method for preparing a light-colored PVC positive mold outer layer resistant to yellowing and its product. Background Technology

[0002] PVC artificial leather has been developed in the synthetic leather industry for many years, but the problem of yellowing and aging of products has always existed, especially for light-colored products. Improving their long-term light and heat resistance has always been a major challenge for researchers. Yellowing occurs during long-term testing of light-colored PVC positive mold surfaces after production line sampling / testing of prototype parts manufactured for clients. Existing technologies are mostly applied to black / dark PVC positive mold surfaces. For black / dark PVC surfaces, the addition of pigments (most black / dark PVC surfaces contain carbon black) makes the performance more stable than light-colored materials, reducing the penetration and effect of light and heat on the PVC substrate and mitigating yellowing caused by light and heat-induced oxidation. Light-colored surface materials have a higher titanium dioxide content, which has higher photocatalytic activity. Under long-term testing conditions, this can cause oxidative degradation of the PVC molecular chains, leading to yellowing of the PVC positive mold surface. In recent years, more and more car models have adopted light-colored interiors, but their development is limited by the yellowing problem.

[0003] Currently, the light-colored interior materials commonly used in automotive interiors primarily employ polymer resins such as PVC resin powder, reinforced PP, ABS / PC, or blends of styrene / maleic anhydride for the outer layer, while the foam layer mainly uses polyurethane foam or polypropylene foam. The yellowing of PVC artificial leather is influenced by many factors. PVC resin is a heat-sensitive plastic with poor light stability; under the influence of heat and light, the side chains undergo dehydrochlorination. Polyene molecules, when the number of conjugated double bonds in the main chain is not excessive, produce slight color differences. Hydrogen chloride first reacts with surrounding potentially acid-reactive substances, and its conjugated double bonds become new active sites within the PVC molecular chain. After being photoinitiated into large molecular free radicals, PVC is easily oxidized, resulting in color changes. Secondly, the presence of a certain amount of low molecular weight components in PVC resin reduces the polymer's thermal stability. The decomposition mechanisms of PVC include free radical mechanisms, ionic mechanisms, and unimolecular mechanisms. Besides stabilizers, PVC decomposition may also be affected by the quality of the PVC resin itself, such as whether there is excessive residual initiator within the PVC resin. If there are certain impurities in the polymer, such as initiators, catalysts, acids, or alkalis added during the polymerization process that cannot be completely removed, or if the polymer absorbs moisture during storage, the stability of the polymer will be reduced.

[0004] The current solution to the yellowing problem of light-colored PVC positive mold skin is to add additives such as amine-resistant agents, heat stabilizers, light stabilizers, antioxidants, and ultraviolet absorbers to the formula. Adding these additives can indeed extend the service life to a certain extent. However, the "saturation effect" of each additive means that once the content of the added material reaches a certain threshold, the yellowing resistance does not change significantly with increasing content, making it difficult to achieve further breakthroughs. This has created new obstacles for the development of light-colored PVC positive mold skin.

[0005] Therefore, to improve the research on light-colored PVC positive mold skin, it is urgent to develop new methods to enhance the stability of its long-term testing experiments, thereby optimizing the yellowing problem. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing a light-colored PVC positive mold skin resistant to yellowing and the product thereof, so as to solve the problem that the yellowing resistance of light-colored PVC positive mold skin is difficult to improve after encountering the saturation effect of additives.

[0007] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing a light-colored PVC positive mold skin resistant to yellowing, comprising the following:

[0008] Weigh out 100 parts by weight of PVC resin powder, 40-50 parts of plasticizer, 4-6 parts of epoxy heat-resistant plasticizer, 2-4 parts of heat stabilizer, 2-4 parts of flame retardant, 2-3 parts of PVC layer lubricant, 10-20 parts of filler, 0.1-0.5 parts of ultraviolet absorber, heat-resistant additives, amine-resistant additives, and heat-resistant pigments, wherein the weight ratio of PVC resin powder, heat-resistant additives, amine-resistant additives, and heat-resistant pigments is 100:0.5a:0.5a:0.3a, where a is 2-4; after mixing, the mixture is melt-extruded, cast into a film, and cooled and molded to obtain a modified PVC skin layer; According to the weight percentages, 90-95 parts of polypropylene, 3-5 parts of foaming agent, 0.6-1 parts of amine catalyst, 0.3-0.5 parts of antioxidant, and 0.2-0.4 parts of foaming layer lubricant are blended, melt extruded and foamed, molded, and cooled to obtain a foamed layer. The modified PVC skin layer and the foamed layer are bonded together with an adhesive. According to the weight proportions, weigh 100 parts of the main film-forming substance, 75-85 parts of the waterborne polyurethane substrate, 3-5 parts of the curing agent, 0.6-1 parts of the leveling agent, and 0.2-0.3 parts of the defoamer, mix them evenly to obtain a coating agent. Apply the coating agent to the side of the modified PVC skin layer away from the foaming layer by roller coating. After drying, a surface coating layer is formed, and a light-colored PVC positive mold skin resistant to yellowing is obtained.

[0009] Preferably, the heat-resistant additives mentioned above are phosphite-based heat-resistant additives, the amine-resistant additives are hindered phenolic amine-resistant additives, and the heat-resistant pigments are, by weight, 9 parts titanium dioxide R-996 and 1 part light-colored heat-resistant iron oxide yellow.

[0010] Preferably, the degree of polymerization of the PVC resin powder is 1300.

[0011] Preferably, the main film-forming substance in the above coating agent is polycarbonate TBC1000, and the solid content of the waterborne polyurethane substrate is 30-40%.

[0012] Another technical solution provided by the present invention: a light-colored PVC positive mold skin resistant to yellowing, prepared by the above preparation method.

[0013] Preferably, the surface of the positive mold is aged in hot air at 90°C for 500 hours and then cooled for 30 minutes. Compared with the control sample placed in a standard environment, the color fastness is evaluated as ≥4 grade according to GB / T 250.

[0014] Preferably, the thickness of the foamed layer is 2.5-3 mm, the thickness of the modified PVC skin layer is 0.8-1.6 mm, and the thickness of the surface coating layer is 0.01-0.05 mm.

[0015] Compared with the prior art, the beneficial effects of the present invention are: This method for preparing light-colored PVC positive mold outer skin with yellowing resistance and its product does not employ complex special processes. Simply by proportionally increasing the content of heat-resistant additives, amine-resistant additives, and heat-resistant pigments in the modified PVC outer skin layer, it overcomes the saturation effect of each material individually. This allows the light-colored PVC positive mold outer skin to achieve a significant leap in yellowing resistance under high-intensity, long-term experimental testing. This confirms that proportionally increasing the content of heat-resistant additives, amine-resistant additives, and heat-resistant pigments has a significant synergistic effect on the modified PVC outer skin layer. The preparation method of this invention overcomes the "saturation effect" of a single additive. When the content of heat-resistant additives, amine-resistant additives, and heat-resistant pigments is increased individually, the yellowing resistance performance does not increase due to the saturation of adsorption / reaction sites within the material. This invention overcomes the technical pain point of ineffective single optimization. The synergistic effect of the three materials allows the color fastness of the light-colored PVC positive mold outer skin to exceed level 4, solving the industry problem of yellowing in light-colored PVC through a simple method. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the material distribution of each layer in this invention.

[0017] In the diagram: 1. Top coating layer; 2. Modified PVC outer skin layer; 3. Foam layer; 4. Back coating layer. Detailed Implementation

[0018] PVC positive mold outer skin generally consists of a PPFoam (polypropylene foam) layer, a PVC dense layer, and a surface treatment layer. The PPFoam layer is made of PP polypropylene with added amine catalysts, foaming to resemble a sponge, providing support, improving feel, and enhancing the material's mechanical tensile properties. The PVC dense layer, or outer skin layer, mainly consists of PVC resin, plasticizers, and fillers. Different color pigments are added to the surface, resulting in different colors for the PVC dense layer. The surface treatment layer is generally a semi-transparent milky white material, mainly composed of polyurethane, which improves the surface layer's abrasion resistance, chemical resistance, photo- and heat aging resistance, and provides a smooth feel. To improve and optimize the yellowing resistance of light-colored PVC positive mold outer skin, this invention mainly targets the saturation effect of the heat-resistant additive content, amine-resistant additive content, and pigment content in the formulation of the PVC dense layer (modified PVC outer skin layer), thus overcoming the yellowing resistance issue of PVC outer skin.

[0019] The materials used in the following comparative examples and embodiments: Modified PVC outer layer: The PVC resin powder used is Xinjiang Tianye New Materials' suspension general-purpose PVC resin (polymerization degree 1300); the plasticizer used is epoxy stearate octyl ester (Lankroflex ED6); the epoxy heat-resistant plasticizer used is Fengyi New Materials' epoxy soybean oil 001; the heat stabilizer used is PVC-specific calcium-zinc composite stabilizer CZ-101; the flame retardant used is antimony trioxide; the PVC layer lubricant used is 1 part stearic acid and 1.5 parts PE wax by weight; the filler used is 3 parts calcium carbonate whiskers (30±5μm, aspect ratio 25±5, purity ≥98%) and 1 part calcium sulfate granules (200 mesh, purity ≥99%) by weight; the ultraviolet absorber used is UV-531; the heat-resistant additive used is phosphite heat-resistant additive 168; and the amine-resistant additive used is Irganox 565. Foaming layer: Polypropylene is Sinopec Maoming HT9025NX, foaming agent is azobisformamide, amine catalyst is azodimethylamide, antioxidant is antioxidant 1010, and foaming layer lubricant is calcium stearate. Topcoat: The main film-forming substance is polycarbonate TBC1000 (Precision Coatings Co., Ltd.), the waterborne polyurethane substrate is Ruilin RL-63012A coating agent, the curing agent is HDI trimer curing agent (for waterborne polyurethane), the leveling agent is BYK-333 silicone leveling agent, and the defoamer is BYK-024 polyether defoamer. The back coating is used to bond the skin and skeleton materials and has no effect on yellowing. Therefore, the following comparative examples and embodiments do not involve back coating processing. In actual production and use, polyurethane adhesive or curing agent can be used.

[0020] For details on the distribution of materials in each layer, please refer to [link / reference]. Figure 1 .

[0021] Comparative Example 1 Weigh out 100 parts by weight of PVC resin powder, 45 parts of plasticizer, 5 parts of epoxy heat-resistant plasticizer, 3 parts of heat stabilizer, 3 parts of flame retardant, 2.5 parts of PVC layer lubricant, 15 parts of filler, 0.3 parts of ultraviolet absorber, 0.5 parts of heat-resistant additive, 0.5 parts of amine-resistant additive, and 0.3 parts of heat-resistant pigment; mix them, then melt-extrude, cast into a film, and cool to form a modified PVC skin layer. According to the weight percentage, 93 parts of polypropylene, 4 parts of foaming agent, 0.8 parts of amine catalyst, 0.4 parts of antioxidant, and 0.3 parts of foaming layer lubricant are blended, melt extruded and foamed, molded, and cooled to obtain a foamed layer. The modified PVC skin layer and the foamed layer are bonded together with an adhesive. According to the weight proportions, 100 parts of the main film-forming substance, 80 parts of water-based polyurethane substrate, 4 parts of curing agent, 0.8 parts of leveling agent, and 0.2 parts of defoamer are weighed and mixed evenly to obtain a coating agent. The coating agent is applied to the modified PVC skin layer on the side away from the foaming layer by roller coating. After drying, a surface coating layer is formed to obtain a light-colored PVC positive mold skin.

[0022] Comparative Example 2 Based on Comparative Example 1, the heat-resistant additive was increased to 1 part, while all other steps remained the same as in Comparative Example 1.

[0023] Comparative Example 3 Based on Comparative Example 1, the heat-resistant additive was increased to 2 parts, while all other steps remained the same as in Comparative Example 1.

[0024] Comparative Example 4 Based on Comparative Example 1, the amount of amine-resistant additive was increased to 1 part, while all other steps remained the same as in Comparative Example 1.

[0025] Comparative Example 5 Based on Comparative Example 1, the amount of amine-resistant additive was increased to 2 parts, while all other steps remained the same as in Comparative Example 1.

[0026] Comparative Example 6 Based on Comparative Example 1, the amount of heat-resistant pigment was increased to 0.6 parts, while all other steps remained the same as in Comparative Example 1.

[0027] Comparative Example 7 Based on Comparative Example 1, the amount of heat-resistant pigment was increased to 1.2 parts, while all other steps remained the same as in Comparative Example 1.

[0028] Example 1 Based on Comparative Example 1, the heat-resistant additive was increased to 1 part, the amine-resistant additive was increased to 1 part, and the heat-resistant pigment was increased to 0.6 parts, while all other steps remained the same as in Comparative Example 1.

[0029] Example 2 Based on Comparative Example 1, the heat-resistant additive was increased to 2 parts, the amine-resistant additive was increased to 2 parts, and the heat-resistant pigment was increased to 1.2 parts, while all other steps remained the same as in Comparative Example 1.

[0030] The heat resistance and light resistance properties of the examples and comparative examples were tested respectively. The testing equipment was as follows: Hot Air Aging Chamber: QH-1000, Shanghai Suying Test Instrument Co., Ltd. Xenon Lamp Test Chamber: CZ-062B, Wenzhou Chengzhi Electromechanical Instrument Equipment Co., Ltd. Standard light source box: CAC-600, Shenzhen Jiabiao Light Source Technology Development Co., Ltd. Spectrophotometer: CM-25, Konica Minolta Heat resistance test: Take a size of 210mm Four PVC positive mold skins were made with a diameter of 297mm. One sample was placed in a standard environment (temperature: 23℃±2℃, humidity: 50%RH±5%RH) as a standard sample. The other three samples were tested according to the TL 496 standard method, specifically by placing them in a 90℃ hot air aging chamber for 500 hours. After the storage experiment, the samples were removed and cooled to room temperature for 30 minutes. They were then compared with the standard sample, and the color data of ΔL, Δa, and Δb were measured and recorded. The color difference meter was used with a standard light source of D65 and 10°. The color change grade was evaluated according to GB / T 250, requiring a color fastness of ≥4.

[0031] Lightfastness test: Take a size of 30mm Four PVC positive mold skins made with an 80mm diameter were used. One sample was placed in a standard environment (temperature: 23℃±2℃, humidity: 50%RH±5%RH) as a standard sample. The other three samples were tested according to the TL 496PV1303 standard method, with the following specific conditions: black mark temperature: 100±3℃, chamber temperature: 65±3℃, relative humidity inside the chamber: 20±10%, irradiance: 300~400 mm (60W / m²). 2 ), Filtering system: Xenochrom 320, Total experimental energy: 70 MJ / m 2After the experiment, the sample was taken out and cooled at room temperature for 30 minutes. It was then compared with the standard sample. The color data of △L, △a, and △b of the PVC skin sample were tested and recorded. The color difference meter was used with a standard light source of D65 and 10°. The color change level was evaluated according to GB / T 250, and the color fastness was required to be ≥4.

[0032] Table 1. Results of heat resistance and light resistance tests for comparative examples and embodiments.

[0033] As shown in Table 1, the values ​​of ΔL, Δa, and Δb all changed to varying degrees after the heat resistance test, with the change in Δb being the most obvious, showing a clear yellowing of the sample. Compared to Comparative Example 1, in Comparative Example 2, the heat resistance of the modified PVC skin layer was significantly improved after the content of the heat-resistant additive in the modified PVC skin layer was increased by 2 times; compared to Comparative Example 2, in Comparative Example 3, further increasing the content of the heat-resistant additive did not improve the heat resistance at all. This indicates that once the content of heat-resistant additives in the modified PVC skin layer reaches a certain value, the yellowing resistance will no longer show a significant improvement with the increase of heat-resistant additives. Under ultraviolet light, heat, and oxygen in the air, PVC will accelerate the initiation of impurities (catalysts, initiators, etc.) remaining from the polymerization process. The resulting free radicals attack the -CH2 chain segment, causing PVC degradation. These free radicals combine with -Cl single bonds to form HCl, releasing hydrogen chloride and gradually forming polyolefin conjugated double bonds. With the increase of continuous conjugated double bonds, PVC turns yellow. Simultaneously, polypropylene materials release amine catalysts (azobisformamide) added during the foaming process at high temperatures, accelerating the dehydrochlorination reaction of PVC, further accelerating PVC degradation and exacerbating the yellowing phenomenon. Increasing the amount of heat-resistant additives in PVC can improve the degradation rate of PVC at high temperatures and effectively reduce the dehydrochlorination reaction. When the heat-resistant additive reaches a certain content, the material is in a saturated state. Further increasing the amount of heat-resistant additive will result in less and less improvement in the yellowing resistance. In summary, it can be seen from Comparative Examples 1 to 3 that 1 part of heat-resistant additive is close to saturation.

[0034] Compared to Comparative Example 1, in Comparative Example 4, after the content of amine-resistant additive in the modified PVC skin layer was increased by 2 times, the lightfastness and heat resistance of the leather were significantly improved. This indicates that the yellowing resistance of PVC leather was significantly improved, mainly because the addition of amine-resistant additives inhibited the degradation catalytic dehydrochlorination reaction of PVC by the -NH3 segment, and the -Cl segment combined with the -NH3 to form chlorate components, eliminating the catalytic effect of HCl on PVC degradation. Compared to Comparative Example 5, the improvement in yellowing resistance of the skin layer with the increase of amine-resistant additive content was not as significant as in Comparative Examples 1 and 4. This indicates that when the amine-resistant additive reaches 1 part, the material is already close to saturation, and further increasing the amount of amine-resistant additive will result in less and less improvement in yellowing resistance.

[0035] As the content of heat-resistant pigment increased, the experimental test results improved. Comparing Comparative Example 1 and Comparative Example 6, when the pigment content was increased to twice the original amount, ΔL, Δa, and Δb in the dense layer all showed significant improvement. This is because as the pigment content increases, the color of the modified PVC skin layer tends to darken, which improves its resistance to aging reactions caused by ultraviolet light, heat, and oxygen in the air. Comparing Comparative Example 6 and Comparative Example 7, when the pigment content was increased to four times that of Comparative Example 1, the test results showed no change in the resistance to yellowing. Similarly, it can be seen that 0.6 parts of heat-resistant pigment is also basically in a saturated state.

[0036] However, in Examples 1 and 2 of this invention, three materials were added to the three saturation states mentioned above, and it was unexpectedly found that the saturation effect could be broken. Compared with Example 1, when the contents of heat-resistant additive, amine-resistant additive, and heat-resistant pigment were increased to twice that of Comparative Example 1, the yellowing resistance of the modified PVC skin layer was significantly improved, especially the heat resistance performance, which reached an unprecedented level and met the basic requirement of ≥4 level. In Example 2, the three materials were increased to four times that of Comparative Example 1, and the heat resistance performance further broke through level 4, which is obviously no longer limited to the saturation effect range of the three materials.

[0037] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope defined in the claims.

[0038] Any aspects of this invention not described in detail are well-known to those skilled in the art.

Claims

1. A method for preparing a light-colored PVC positive mold skin resistant to yellowing, characterized in that, Includes the following: Weigh out 100 parts by weight of PVC resin powder, 40-50 parts of plasticizer, 4-6 parts of epoxy heat-resistant plasticizer, 2-4 parts of heat stabilizer, 2-4 parts of flame retardant, 2-3 parts of PVC layer lubricant, 10-20 parts of filler, 0.1-0.5 parts of ultraviolet absorber, heat-resistant additives, amine-resistant additives, and heat-resistant pigments, wherein the weight ratio of PVC resin powder, heat-resistant additives, amine-resistant additives, and heat-resistant pigments is 100:0.5a:0.5a:0.3a, where a is 2-4; after mixing, the mixture is melt-extruded, cast into a film, and cooled and molded to obtain a modified PVC skin layer; According to the weight percentage, 90-95 parts of polypropylene, 3-5 parts of foaming agent, 0.6-1 parts of amine catalyst, 0.3-0.5 parts of antioxidant, and 0.2-0.4 parts of foaming layer lubricant are mixed, and then melt-extruded, foamed, molded, and cooled to obtain a foamed layer. The modified PVC skin layer and the foamed layer are bonded together with an adhesive. According to the weight proportions, weigh 100 parts of the main film-forming substance, 75-85 parts of the waterborne polyurethane substrate, 3-5 parts of the curing agent, 0.6-1 parts of the leveling agent, and 0.2-0.3 parts of the defoamer, mix them evenly to obtain a coating agent. Apply the coating agent to the side of the modified PVC skin layer away from the foaming layer by roller coating. After drying, a surface coating layer is formed, and a light-colored PVC positive mold skin resistant to yellowing is obtained.

2. The method for preparing a light-colored PVC positive mold skin resistant to yellowing according to claim 1, characterized in that: The heat-resistant additives are phosphite-based heat-resistant additives, the amine-resistant additives are hindered phenolic amine-resistant additives, and the heat-resistant pigments are, by weight, 9 parts titanium dioxide R-996 and 1 part light-colored heat-resistant iron oxide yellow.

3. The method for preparing a light-colored PVC positive mold skin resistant to yellowing according to claim 1, characterized in that: The degree of polymerization of the PVC resin powder is 1300.

4. The method for preparing a light-colored PVC positive mold skin resistant to yellowing according to claim 1, characterized in that: The main film-forming substance in the coating agent is polycarbonate TBC1000, and the solid content of the waterborne polyurethane substrate is 30-40%.

5. A light-colored PVC positive mold skin resistant to yellowing, prepared by the preparation method according to any one of claims 1 to 4.

6. The light-colored PVC positive mold outer skin resistant to yellowing according to claim 5, characterized in that: The surface of the positive mold was aged in hot air at 90℃ for 500 hours, cooled for 30 minutes, and compared with the control sample placed in a standard environment. The color fastness was evaluated according to GB / T 250 as ≥4 grade.

7. The light-colored PVC positive mold outer skin resistant to yellowing as described in claim 5, characterized in that: The thickness of the foamed layer is 2.5–3 mm, the thickness of the modified PVC skin layer is 0.8–1.6 mm, and the thickness of the surface coating layer is 0.01–0.05 mm.

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