A method for preparing a water-soluble film

Abstract

A method for preparing a water-soluble film belongs to the technical field of water-soluble films and comprises the following steps: A. weighing raw materials, including 80-120 parts by mass of nano-calcium carbonate-modified polyvinyl alcohol and 1-10 parts of filler; B. processing the raw materials weighed in step A by a casting process to obtain a water-soluble film; the specific process parameters of the casting process are: the temperature of the barrel zone is 160-200°C, the temperature of the connector, screen changer, and elbow is 205-210°C, the temperature of the die zone is 190-195°C, and the mesh size of the screen is 125-175 mesh. By using nano-calcium carbonate-modified polyvinyl alcohol and nano-silicon dioxide as the raw materials for the water-soluble film, the present invention reduces the melting point of polyvinyl alcohol from the original 230-240°C to about 180°C, increases the decomposition temperature to about 210°C, increases the process temperature adjustable range, and makes production more stable.

Description

Technical Field

[0001] The invention belongs to the technical field of water-soluble films, and particularly relates to a method for preparing a water-soluble film. Background Art

[0002] Existing film production processes are generally blow molding and cast film processes. Compared with blown films, films produced by cast film processes have uniform film thickness, good transparency and good heat sealing properties.

[0003] However, the main component of the currently used water-soluble film is polyvinyl alcohol. The melting temperature of polyvinyl alcohol itself (230℃-240℃) is very close to the decomposition temperature (200℃). The adjustable range of process temperature during the casting process is very narrow. The modulus of polyvinyl alcohol is high, which leads to high friction heat in the water-soluble film during the casting process. As a result, the production temperature always has a large floating range. The instability of this floating range makes the processing of the water-soluble film difficult, and the prepared water-soluble film is prone to yellowing. Summary of the Invention

[0004] To address the aforementioned problems in the prior art, the present invention provides a method for preparing a water-soluble film. By using nano-calcium carbonate-modified polyvinyl alcohol and nano-silicon dioxide as the raw materials for the water-soluble film, the present invention reduces the melting point of polyvinyl alcohol from 230°C-240°C to approximately 180°C and increases the decomposition temperature to approximately 210°C, thereby increasing the process temperature adjustable range and making production more stable.

[0005] The specific technical solution adopted in the present invention is:

[0006] A method for preparing a water-soluble film comprises the following steps:

[0007] A. Weigh the raw materials, including 80-120 parts of nano-calcium carbonate modified polyvinyl alcohol and 1-10 parts of filler by mass;

[0008] B. Processing the raw materials weighed in step A by a casting process to obtain a water-soluble film;

[0009] The specific process parameters of the casting process are: the temperature of the barrel area is 160-200°C, the temperature of the connector, screen changer and elbow is 205-210°C, the temperature of the die area is 190-195°C, and the mesh number of the screen is 125-175 mesh.

[0010] Furthermore, the filler includes nano-silicon dioxide.

[0011] Furthermore, the screen is a steel woven screen.

[0012] Furthermore, the screen is a single-layer screen.

[0013] The beneficial effects of the present invention are:

[0014] 1. The present invention adopts nano-calcium carbonate to modify polyvinyl alcohol, so that the melting point of polyvinyl alcohol is reduced from the original 230℃-240℃ to about 180℃. Since the decomposition temperature of polyvinyl alcohol in the prior art is lower than the melting point, polyvinyl alcohol is partially decomposed during the casting process and melts only after decomposing to a certain extent. Since decomposition must occur before melting, the prepared water-soluble film has the problem of yellowing. The nano-calcium carbonate modified polyvinyl alcohol of the present invention utilizes the properties of calcium carbonate to reduce the force between PVA molecules, thereby relatively lowering the melting point of PVA and making the melting point of polyvinyl alcohol lower than its decomposition temperature, making the process The temperature adjustable range is increased, and the prepared water-soluble film will not turn yellow. At the same time, nano-silicon dioxide is added to the raw materials of the present invention. The addition of nano-silicon dioxide increases the decomposition temperature of the nano-calcium carbonate-modified polyvinyl alcohol-silicon dioxide composite material, and no decomposition phenomenon occurs within a temperature range of 210° C., further increasing the process temperature adjustable range, making production more stable, and better able to resist temperature fluctuations caused by frictional heat generation, and not prone to yellowing. Because the faster the screw speed, the greater the frictional heat generated. By increasing the difference between the melting point and the decomposition temperature, the processing efficiency can also be improved, and the production speed can be increased to 80 m / min.

[0015] 2. The water-soluble film preparation method of the present invention will not cause die head breakage and other phenomena during the preparation process. The prior art generally uses a multi-layer steel woven screen with a mesh size of 300 / 150 / 300 to block color spots caused by poor plasticization. However, because the modulus of polyvinyl alcohol is large, the pressure in the barrel itself is very large. The use of multi-layer screens in the prior art will lead to excessive pressure in front of the screen, causing the raw material to stay in the barrel for too long and cause decomposition. Excessive screen pressure will also lead to failure to extrude the material, die head breakage and other phenomena. Therefore, the present invention reduces the mesh size and quantity of the screen, and adopts a single-layer screen with a mesh size of about 150, which reduces the screen pressure, makes the discharge smoother, and reduces the number of screens used, thereby reducing production costs and improving production efficiency.

[0016] However, experiments have shown that reducing the mesh size and number of screens will result in a large number of poorly plasticized color spots flowing out, affecting product quality. In the prior art, due to the small adjustable temperature range of the casting process, the temperature of the barrel area is the same as the temperature of the connector, screen changer, elbow, and die area. The present invention improves the adjustable temperature range of the casting process by using a nano-calcium carbonate-modified polyvinyl alcohol-silicon dioxide composite material. Based on this beneficial effect, the temperature of the connector, screen changer, and elbow is increased. After the temperature is increased, the poorly plasticized color spots will undergo a melting process. After passing through the connector, screen changer, and elbow flow channel, the color spots slowly melt, thereby reducing the generation of color spots.

[0017] 3. The water-soluble film of the present invention has a more uniform film thickness. In the prior art, the temperature of the barrel zone is the same as the temperature of the connector, screen changer, elbow, and die zone. On the one hand, this is limited by the small adjustable temperature range of the casting process in the prior art. On the other hand, different temperatures will affect the flow of the molten raw materials and cause unstable quality. However, researchers have found that lowering the die temperature can make the molten raw materials more evenly spread in the mold cavity. When the die temperature is the same as the temperature of the elbow and connector, the film will have uneven thickness due to the excessive fluidity of the molten fluid. After lowering the die temperature, this phenomenon is alleviated, and the thickness of the prepared film is more uniform. DETAILED DESCRIPTION

[0018] In the present invention, other raw materials used can be purchased from the market unless otherwise specified. 1. Specific embodiments

[0020] Example 1

[0021] A. Weigh the raw materials, including 100 parts of nano-calcium carbonate-modified polyvinyl alcohol and 5 parts of nano-silicon dioxide, by mass.

[0022] B. Processing the raw materials weighed in step A by a casting process to obtain a water-soluble film;

[0023] The specific process parameters of the casting process are: the temperature of the barrel 1-8 zones is 170-200°C increasing, the temperature of the connector, screen changer and elbow is 208°C, the temperature of the die zone is 192°C, and the screen is a 150-mesh single-layer steel woven screen.

[0024] Example 2

[0025] A. Weigh the raw materials, including 80 parts by mass of nano-calcium carbonate-modified polyvinyl alcohol and 1 part of nano-silicon dioxide;

[0026] B. Processing the raw materials weighed in step A by a casting process to obtain a water-soluble film;

[0027] The specific process parameters of the casting process are: the temperature of the barrel 1-8 zones is 160-200°C in increments, the temperature of the connector, screen changer, and elbow is 205°C, the temperature of the die zone is 190°C, and the screen is a 175-mesh single-layer steel woven screen.

[0028] Example 3

[0029] A. Weigh the raw materials, including 120 parts of nano-calcium carbonate-modified polyvinyl alcohol and 10 parts of nano-silicon dioxide, by mass.

[0030] B. Processing the raw materials weighed in step A by a casting process to obtain a water-soluble film;

[0031] The specific process parameters of the casting process are: the temperature of the barrel 1-8 zones is 165-200°C in increments, the temperature of the connector, screen changer, and elbow is 210°C, the temperature of the die zone is 195°C, and the screen is a 175-mesh single-layer steel woven screen.

[0032] Comparative Example 1

[0033] The only difference between Comparative Example 1 and Example 1 is that nano-silicon dioxide is not added in Comparative Example 1.

[0034] Comparative Example 2

[0035] The only difference between Comparative Example 2 and Example 1 is that the temperature of the die zone in Comparative Example 2 is 208°C.

[0036] Comparative Example 3

[0037] The only difference between Comparative Example 3 and Example 1 is that a three-layer steel woven screen with mesh sizes of 300 / 150 / 300 is used in Comparative Example 3.

[0038] 2. Performance Testing

[0039] The performance of the water-soluble films prepared in the above examples and comparative examples was tested.

[0040] The film thickness uniformity test method is: take a point every 50cm on the sample, measure the thickness of 5 points respectively, and calculate the maximum deviation between the thickest point or the thinnest point of the film and the average thickness;

[0041] The yellowing rate is tested by a color difference index, with the water-soluble film prepared in Example 1 as the base color value 0, adding a value relative to the yellowing of the water-soluble film prepared in Example 1, and subtracting a value relative to the transparency of the water-soluble film prepared in Example 1.

[0042] Color point content test method: Randomly mark 5 square areas with a side length of 5 cm on the film and calculate the average value of the color points in the area.

[0043]

[0044] From the comparison between Example 1 and Comparative Example 1, it can be seen that the addition of silicon dioxide in Example 1 increases the difference between the melting temperature and the decomposition temperature, expands the adjustable range of the process temperature, and does not produce decomposition within the temperature range of 210°C. Polyvinyl alcohol is not easily decomposed, so that the film is not easy to turn yellow.

[0045] By comparing Example 1 with Comparative Example 2, it can be seen that after lowering the temperature of the die area in Example 1, the film thickness is more uniform. This is because lowering the die temperature allows the molten raw material to be spread more evenly in the mold cavity. If the die temperature is not lowered, and the die temperature is the same as the temperature of the elbow and the connector, the fluidity of the molten fluid is too good, resulting in uneven film thickness.

[0046] From the comparison between Example 1 and Comparative Example 3, it can be seen that the material breaking phenomenon occurred in Comparative Example 3, and the color difference index was higher. This is because the modulus of PVA is larger and the production pressure in the barrel itself is higher. If the screen is used according to the conventional method, the pressure before the screen will be too high. Excessive screen pressure will also lead to material extrusion failure, die head breakage, etc. At the same time, excessive pressure before the screen will cause the raw material to stay in the barrel for too long, resulting in decomposition and yellowing. Example 1 solves the above problems by reducing the mesh number and the number of layers of the screen. At the same time, by changing the process temperature, the problem of more color points caused by reducing the mesh number of the screen is solved.

Claims

1. A method for preparing a water-soluble film, characterized in that: The following steps are involved: A. Weigh the raw materials, including 80-120 parts of nano-calcium carbonate modified polyvinyl alcohol and 1-10 parts of filler by mass; B. Processing the raw materials weighed in step A by a casting process to obtain a water-soluble film; The specific process parameters of the casting process are: the temperature of the barrel area is 160-200°C, the temperature of the connector, screen changer, and elbow is 205-210°C, the temperature of the die area is 190-195°C, and the mesh size of the screen is 125-175 mesh; The filler includes nano-silicon dioxide.

2. The method for preparing a water-soluble film according to claim 1, wherein: The screen is a steel woven screen.

3. The method for preparing a water-soluble film according to claim 1, wherein: The screen is a single-layer screen.

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