A bichromatic heat-sensitive synthetic paper, a preparation method and application thereof

Abstract

The application belongs to the field of heat-sensitive recording materials, and particularly relates to a dual-color heat-sensitive synthetic paper as well as a preparation method and application thereof. The dual-color heat-sensitive synthetic paper comprises a substrate, and a first color developing layer, a second color developing layer and a protective layer are sequentially arranged on the surface of the substrate. The first color developing layer is composed of 15-30% of a layer of dye, 30-60% of a layer of color developing agent and 10-55% of a layer of adhesive. The second color developing layer is composed of 10-20% of a second layer of filler, 15-20% of a second layer of dye, 20-40% of a second layer of color developing agent, 15-30% of a second layer of adhesive and 10-20% of a heat-insulating polymer material. The protective layer is composed of 30-50% of a protective layer filler, 30-50% of a protective layer adhesive, 5-15% of a lubricant and 3-5% of a curing agent. The dual-color heat-sensitive synthetic paper is clear and stable, has excellent environmental heat interference resistance, can effectively block condensate water penetration, can effectively prevent printed characters and ink printed information from being blurred due to water diffusion, and can be applied in complex scenes with cold, heat and humidity.

Description

Technical Field

[0001] This invention belongs to the field of thermal recording materials, and specifically relates to a two-color thermal synthetic paper, its preparation method, and its application. Background Technology

[0002] Thermal paper is widely used for product labels due to its ease of printing. For beverage labels such as milk tea and coffee, it's often necessary to print the product name, price, and special requirements (such as "less ice" or "add sugar" for emphasis). Two-color printing effectively highlights this key information. Existing two-color thermal paper technologies often employ multi-layered structures for color separation and protection, including designs with up to five layers such as a pre-coating layer, isolation layer, color-developing layer, and protective layer. These layered structures involve complex manufacturing processes, resulting in high production and coating costs. Furthermore, the protective layer may fail when exposed to condensation from cold beverage cups, causing the printed text and images to become blurred due to moisture erosion. Simultaneously, the complex coating structure may affect the paper's stiffness and printability, and if the thermal system is poorly designed, the label may unexpectedly develop color when in contact with a hot cup due to ambient heat. Therefore, a simpler two-color thermal label material is needed that specifically resists condensation and ensures stability in hot beverage environments. Summary of the Invention

[0003] This invention provides a two-color thermal synthetic paper with clear and stable two-color printing, excellent resistance to environmental thermal interference, and effective blocking of condensation water penetration. It effectively prevents printed text and ink information from spreading and becoming blurred when exposed to water, and can be used in complex scenarios of cold, heat, and humidity.

[0004] The objective of this invention can be achieved through the following technical solutions:

[0005] A two-color thermal synthetic paper includes a substrate, on the surface of which a first color developing layer, a second color developing layer and a protective layer are sequentially disposed;

[0006] The first color-developing layer consists of a layer of dye with a mass ratio of 15-30%, a layer of color developer with a mass ratio of 30-60%, and a layer of adhesive with a mass ratio of 10-55%.

[0007] Preferably, the first color developing layer consists of a dye layer comprising 15% by mass, a color developing agent layer comprising 30% by mass, and an adhesive layer comprising 55% by mass.

[0008] The second color-developing layer is composed of 10-20% by mass of two-layer filler, 15-20% by mass of two-layer dye, 20-40% by mass of two-layer color developer, 15-30% by mass of two-layer adhesive and 10-20% by mass of heat-insulating polymer material.

[0009] Preferably, the second color-developing layer is composed of 15% by mass of a second-layer filler, 20% by mass of a second-layer dye, 30% by mass of a second-layer color developer, 20% by mass of a second-layer adhesive, and 15% by mass of a heat-insulating polymer material.

[0010] The protective layer is composed of 30-50% protective layer filler, 30-50% protective layer adhesive, 5-15% lubricant, and 3-5% curing agent by mass ratio.

[0011] Preferably, the protective layer is composed of 45% protective layer filler, 40% protective layer adhesive, 10% lubricant and 5% curing agent by mass ratio.

[0012] The color development temperature T1 of the first color development layer is controlled at 120-150℃, and the color development temperature T2 of the second color development layer is controlled at 90-110℃. The thermosensitive system design of the first and second color development layers in this invention achieves heat resistance, i.e., resistance to environmental thermal interference. By setting T1 and T2 at temperatures far higher than those of the environmental heat source (such as the wall of a hot beverage cup at <80℃), it is ensured that environmental heat cannot reach the color development threshold of either layer, thereby fundamentally preventing the label from accidentally developing color when in contact with a hot cup.

[0013] Preferably, the substrate is a PP film with a thickness of 30μm-200μm.

[0014] Preferably, the dye layer is 2-(2-4-dimethylamino)-3-methyl-6-diethylaminofluorane; the adhesive layer is styrene-acrylic resin.

[0015] Preferably, the first-layer or second-layer color developer is one of 4-[[4-(2-allyloxy)phenyl]sulfonyl]phenol, 4-hydroxy-4'-benzyloxydiphenyl sulfone, and N-(p-toluenesulfonyl)-N'-(3-p-toluenesulfonyloxyphenyl)urea;

[0016] Further preferred, the first-layer color developer and the second-layer color developer are the same color developer. Using the same color developer has better temperature resistance than using a mixture of color developers.

[0017] Preferably, the second-layer dye is one of 2'-chloro-6'-(diethylamino)fluorane, 3,3-bis(2-methyl-1-octyl-1H-indol-3-yl)phthalide, 3,3-bis(4-dimethylaminophenyl)-6-dimethylaminophenylpeptide, and 6'-diethylamino-2'-dibenzylaminofluorane.

[0018] The second-layer adhesive is acrylic resin.

[0019] Preferably, the second layer of filler is one or a mixture of calcium carbonate, aluminum hydroxide, kaolin, and silicon dioxide;

[0020] Preferably, the heat-insulating polymer material is polystyrene. To achieve temperature isolation from the underlying color development layer, the formulation of this invention incorporates polystyrene, which has a heat-insulating effect. Its function is to form a thermal barrier, ensuring that when low printing energy is applied, heat is insufficient to penetrate this layer and activate the underlying first color development layer; only when high energy is applied can heat overcome the barrier, first causing this layer to develop color, and then conducting to the lower layer, thereby achieving sequential color development of two colors and eliminating the need for a separate isolation layer in existing technologies. Simultaneously, polystyrene has high hiding power at room temperature and transforms into a transparent substance at high temperatures, further improving the contrast of the underlying color development.

[0021] Preferably, the protective layer filler is a mixture of several of calcium carbonate, aluminum hydroxide, kaolin, and silica; the protective layer adhesive is acrylic latex; the lubricant is zinc stearate; and the curing agent is aziridine.

[0022] Preferably, the protective layer filler is a mixture of calcium carbonate and silicon dioxide in a weight ratio of 7-9:1; more preferably, the protective layer filler is a mixture of calcium carbonate and silicon dioxide in a weight ratio of 9:1, and the average particle size of the silicon dioxide is 2-3 μm.

[0023] The protective layer in this invention uses highly absorbent composite fillers and highly cross-linked acrylic latex film-forming agents as a top coating, which improves the anchoring ability of ink and coating while preventing erosion by condensation.

[0024] The preparation method of the above-mentioned two-color thermal synthetic paper includes the following steps:

[0025] S1, First color development layer coating liquid: Weigh and mix the raw materials in the first color development layer according to the ratio to prepare a uniform coating liquid with a solid content of 20-35%.

[0026] S2, Second color development layer coating liquid: Weigh and mix the raw materials in the second color development layer according to the ratio to prepare a uniform coating liquid with a solid content of 20-35%.

[0027] S3, Protective coating liquid: Weigh and mix the raw materials in the protective layer according to the ratio to prepare a uniform coating liquid with a solid content of 10-20%.

[0028] S4. Apply the first color-developing layer coating liquid to the substrate surface in sequence, with a coating weight of 3.5-6 g / m²; apply the second color-developing layer coating liquid, with a coating weight of 3.5-6 g / m²; and apply the protective layer coating liquid, with a coating weight of 1-3 g / m².

[0029] The aforementioned two-color thermal synthetic paper can be used in takeaway labels for hot and cold beverages.

[0030] The beneficial effects of this invention are:

[0031] 1. Simplified and efficient structure: The traditional five-layer or more structure is refined into a core three-layer structure, reducing coating processes and raw material types, improving production efficiency and reducing production costs.

[0032] 2. Clear and stable dual colors: By precisely designing the color development temperature difference between the two color components (T1: 120-150℃, T2: 90-110℃), and embedding polystyrene heat-barrier material in the second color layer, the two colors are effectively separated, and the main and secondary content of the printed content are clearly distinguished.

[0033] 3. Excellent environmental stability:

[0034] Heat interference resistance: Since the color development trigger temperature (T1, T2) is much higher than the ambient heat source temperature, the label will not accidentally develop color when it comes into contact with a hot cup, achieving true "heat resistance" in the usage scenario.

[0035] Condensation resistant: The specially designed protective layer effectively blocks condensation from penetrating, preventing printed text and ink information from spreading and becoming blurred when exposed to water.

[0036] Comprehensive performance adaptation: While ensuring core stability, the structure is simplified and the overall materials are very suitable for the complex usage scenarios of takeaway beverage labels such as milk tea and coffee in alternating cold, hot and humid environments. Detailed Implementation

[0037] The present invention will be further described below with reference to the embodiments:

[0038] Example 1

[0039] 1. Preparation of dye grinding solution: The thermosensitive dye is dispersed and ground to an average particle size of 0.3-0.8μm using a grinder; 30 parts of thermosensitive dye (2-(2-4-dimethylamino)-3-methyl-6-diethylaminofluorane), 30 parts of 10% PVA aqueous solution, and 40 parts of water are used to prepare the dye grinding solution for later use.

[0040] 2. Preparation of color developer grinding slurry: The thermosensitive color developer is dispersed and ground to an average particle size of 0.3-0.8 μm using a grinder; 30 parts of thermosensitive color developer 4-[[4-(2-allyloxy)phenyl]sulfonyl]phenol, 30 parts of 10% PVA aqueous solution, and 40 parts of water are used to prepare the color developer grinding slurry for later use.

[0041] 3. Substrate: 68μm thick white PP.

[0042] 4. First color developing layer coating solution:

[0043] The dye grinding slurry, color developer grinding slurry, and styrene-acrylic resin were rapidly dispersed and mixed to form a uniform coating solution with a solid content of 30%. This solution was then coated onto a PP film with a coating weight of 5 g / m².

[0044] The raw materials in the first color developing layer coating liquid are prepared and mixed in an oven-dry ratio of 15% dye, 30% color developer, and 55% adhesive.

[0045] 5. Second color development layer coating solution:

[0046] The filler is aluminum hydroxide grinding slurry, the dye grinding slurry is 3,3-bis(4-dimethylaminophenyl)-6-dimethylaminophenyl peptide grinding slurry (the preparation method of the dye grinding slurry is the same as in step 1), the thermosensitive color developer is 4-[[4-(2-allyloxy)phenyl]sulfonyl]phenol grinding slurry, and the acrylic resin is used; the heat-insulating polymer composite material is polystyrene. The above components are dispersed and mixed at high speed to form a uniform coating solution with a solid content of 30%, which is then coated on the first color development layer. The coating weight is 5 g / m². 2 .

[0047] The raw materials in the above-mentioned second color developing layer coating liquid are mixed and prepared according to the oven-dry ratio: 15% filler, 20% dye, 30% color developer, 20% adhesive, and 15% polystyrene.

[0048] 6. Protective coating liquid:

[0049] The filler is a mixture of calcium carbonate and silica in a 9:1 ratio; the adhesive is acrylic latex; the lubricant is zinc stearate; and the curing agent is aziridine. The above components are dispersed and mixed at high speed to form a uniform coating liquid with a solid content of 20%. This liquid is then coated above the second color development layer, with a coating weight of 2 g / m². 2 .

[0050] The raw materials in the above protective coating liquid are mixed in an oven-dry ratio: 45% filler, 40% adhesive, 10% lubricant, and 5% curing agent.

[0051] Example 2

[0052] Substrate: 68μm thick white PP;

[0053] The color developer in the first and second color development layer formulations of Example 1 was changed to: N-(p-toluenesulfonyl)-N'-(3-p-toluenesulfonyloxyphenyl)urea; the dye in the second color development layer formulation was changed to: 6'-diethylamino-2'-dibenzylaminofluorane; the other raw materials and their proportions remained unchanged.

[0054] The first color layer, the second color layer, and the protective layer are applied sequentially onto the substrate, with the coating amount of each layer being the same as in Example 1.

[0055] Example 3

[0056] Substrate: 68μm thick white PP;

[0057] In Example 2, the dye in the second colorimetric layer was changed to 3,3-bis(2-methyl-1-octyl-1H-indole-3-yl)phthalide, while the other raw materials and their proportions remained unchanged.

[0058] The first color layer, the second color layer, and the protective layer are applied sequentially onto the substrate, with the coating amount of each layer being the same as in Example 2.

[0059] Example 4

[0060] Substrate: 68μm thick white PP;

[0061] The colorimetric agents in the first and second colorimetric layers in Example 1 were changed to N-(p-toluenesulfonyl)-N'-(3-p-toluenesulfonyloxyphenyl)urea, while the other raw materials and their proportions remained unchanged.

[0062] The first color layer, the second color layer, and the protective layer are applied sequentially onto the substrate, with the coating amount of each layer being the same as in Example 1.

[0063] Comparative Example 1:

[0064] Substrate: 68μm thick white PP;

[0065] The colorimetric agent in the first and second colorimetric layers of Example 1 was changed to 2,4-diphenylsulfone phenol, while the other raw materials and their proportions remained unchanged.

[0066] The first color layer, the second color layer, and the protective layer are applied sequentially onto the substrate, with the coating amount of each layer being the same as in Example 1.

[0067] Comparative Example 2

[0068] Substrate: 68μm thick white PP;

[0069] The filler in the protective layer formulation of Example 1 was replaced with calcium carbonate, while the other raw materials and their proportions remained unchanged.

[0070] The first color layer, the second color layer, and the protective layer are applied sequentially onto the substrate, with the coating amount of each layer being the same as in Example 1.

[0071] Comparative Example 3:

[0072] Substrate: 68μm thick white PP;

[0073] In Example 2, the polystyrene polymer composite material of the second color layer was replaced with an equal amount of aluminum hydroxide, while the other raw materials and their proportions remained unchanged.

[0074] The first color layer, the second color layer, and the protective layer are applied sequentially onto the substrate, with the coating amount of each layer being the same as in Example 2.

[0075] Comparative Example 4:

[0076] Substrate: 68μm thick white PP;

[0077] The colorimetric agent of the first colorimetric layer in Example 1 was changed to N-(p-toluenesulfonyl)-N'-(3-p-toluenesulfonyloxyphenyl)urea, while the other raw materials and their proportions remained unchanged.

[0078] The first color layer, the second color layer, and the protective layer are applied sequentially onto the substrate, with the coating amount of each layer being the same as in Example 1.

[0079] Comparative Example 5:

[0080] Substrate: 68μm thick white PP;

[0081] The colorimetric agent of the second colorimetric layer in Example 1 was changed to N-(p-toluenesulfonyl)-N'-(3-p-toluenesulfonyloxyphenyl)urea, while the other raw materials and their proportions remained unchanged.

[0082] The first color layer, the second color layer, and the protective layer are applied sequentially onto the substrate, with the coating amount of each layer being the same as in Example 1.

[0083] Analysis of experimental results:

[0084] Environmental heat resistance test: A blank finished product label was attached to the outer surface of a paper cup containing hot water at 80±5℃ for 5 minutes, and the OD value of the blank sample was tested with an X-Rite color density meter and found to be <0.15.

[0085] Condensation resistance test: After the above blank sample is printed with UV super color flexographic printing, it is attached to the outer wall of a paper cup filled with ice water. After being placed at room temperature for 10-15 minutes, when condensation appears on the printed surface, the ink surface is rubbed with an index finger wrapped with non-woven fabric more than 30 times without obvious ink falling off.

[0086] Two-color printing test: When tested with a two-color thermal printer, the high-temperature black regular text and the low-temperature blue (red, green) tone text can be clearly distinguished.

[0087] Test results: Two-color printer model: Brother QL-820 / Gprinter GS-2208D two-color printer.

[0088] Example Printing effect OD at 85℃ (blank area) < 0.15 Ink resistant to condensation >30 times Example 1 blue and black 0.09 30 OKs Example 2 Green and Black 0.11 30 OKs Example 3 Red and black 0.11 30 OKs Example 4 blue and black 0.12 30 OKs Comparative Example 1 blue and black 0.45 NG 30 OKs Comparative Example 2 blue and black 0.10 11 NGs Comparative Example 3 Blue-black (NG) (black lettering faded to white) 0.11 30 OKs Comparative Example 4 blue and black 0.23 NG 30 OKs Comparative Example 5 blue and black 0.25 NG 30 OKs

[0089] The test results show that the inks in all four examples have excellent resistance to condensation and temperature resistance up to 85°C, with Example 1 showing particularly good performance.

[0090] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any form or substance. It should be noted that those skilled in the art can make various improvements and additions without departing from the method of the present invention, and these improvements and additions should also be considered within the scope of protection of the present invention. Any modifications, alterations, and equivalent changes made by those skilled in the art based on the above-disclosed technical content without departing from the spirit and scope of the present invention are equivalent embodiments of the present invention. Furthermore, any modifications, alterations, and evolutions made to the above embodiments based on the essential technology of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A two-color thermal synthetic paper, comprising a substrate, characterized in that: A first color-developing layer, a second color-developing layer, and a protective layer are sequentially provided on the surface of the substrate. The first color-developing layer consists of a layer of dye with a mass ratio of 15-30%, a layer of color developer with a mass ratio of 30-60%, and a layer of adhesive with a mass ratio of 10-55%. The second color-developing layer is composed of 10-20% by mass of two-layer filler, 15-20% by mass of two-layer dye, 20-40% by mass of two-layer color developer, 15-30% by mass of two-layer adhesive and 10-20% by mass of heat-insulating polymer material. The protective layer is composed of 30-50% protective layer filler, 30-50% protective layer adhesive, 5-15% lubricant, and 3-5% curing agent by mass ratio. The color development temperature of the first color development layer is controlled at 120-150℃, and the color development temperature of the second color development layer is controlled at 90-110℃.

2. The two-color thermal synthetic paper according to claim 1, characterized in that: The substrate is a PP film with a thickness of 30μm-200μm.

3. The two-color thermal synthetic paper according to claim 1, characterized in that: The dye layer is 2-(2-4-dimethylamino)-3-methyl-6-diethylaminofluorane; the adhesive layer is styrene-acrylic resin.

4. The two-color thermal synthetic paper according to claim 1, characterized in that: The first-layer or second-layer color developer is one of 4-[[4-(2-allyloxy)phenyl]sulfonyl]phenol, 4-hydroxy-4'-benzyloxydiphenyl sulfone, and N-(p-toluenesulfonyl)-N'-(3-p-toluenesulfonyloxyphenyl)urea; preferably, the first-layer and second-layer color developers are the same color developer.

5. The two-color thermal synthetic paper according to claim 1, characterized in that: The second-layer dye is one of 2'-chloro-6'-(diethylamino)fluorane, 3,3-bis(2-methyl-1-octyl-1H-indol-3-yl)phthalide, 3,3-bis(4-dimethylaminophenyl)-6-dimethylaminophenylpeptide, or 6'-diethylamino-2'-dibenzylaminofluorane; the second-layer adhesive is acrylic resin.

6. The two-color thermal synthetic paper according to claim 1, characterized in that: The second layer of filler is one or a mixture of calcium carbonate, aluminum hydroxide, kaolin, and silicon dioxide; the heat-insulating polymer material is polystyrene.

7. The two-color thermal synthetic paper according to claim 1, characterized in that: The protective layer filler is a mixture of several of the following: calcium carbonate, aluminum hydroxide, kaolin, or silica; the protective layer adhesive is acrylic latex; the lubricant is zinc stearate; and the curing agent is aziridine.

8. The two-color thermal synthetic paper according to claim 7, characterized in that: The protective layer filler is a mixture of calcium carbonate and silicon dioxide in a weight ratio of 7-9:1; preferably, the protective layer filler is a mixture of calcium carbonate and silicon dioxide in a weight ratio of 9:

1.

9. A method for preparing the two-color thermal synthetic paper as described in claim 1, comprising the following steps: S1, First color development layer coating liquid: Weigh and mix the raw materials in the first color development layer according to the ratio to prepare a uniform coating liquid with a solid content of 20-35%. S2, Second color development layer coating liquid: Weigh and mix the raw materials in the second color development layer according to the ratio to prepare a uniform coating liquid with a solid content of 20-35%. S3, Protective coating liquid: Weigh and mix the raw materials in the protective layer according to the ratio to prepare a uniform coating liquid with a solid content of 10-20%. S4. Apply the first color-developing layer coating liquid to the substrate surface in sequence, with a coating weight of 3.5-6 g / m², apply the second color-developing layer coating liquid, with a coating weight of 3.5-6 g / m², and apply the protective layer coating liquid, with a coating weight of 1-3 g / m².

10. The application of the two-color thermal synthetic paper as described in claim 1 in the labeling of cold and hot beverage takeaways.