A process and apparatus for extrusion coating of low melt strength plastics

Abstract

The application discloses a process for extrusion coating of low melt strength plastic, comprising the following steps: step one, an extrusion step, extruding a coating layer from a die of an extruder; step two, a heat preservation step, the coating layer extending through a flat die lip extension channel; and step three, a lamination step, the coating layer being compounded with a substrate in a lamination area. The process and the device for extrusion coating of low melt strength plastic can improve the processing speed of low melt strength plastic such as polylactic acid as the coating layer, and reduce the production cost.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of composite film processing, in particular to a process and device for extrusion coating of low melt strength plastic. BACKGROUND

[0002] Polylactic acid is derived from lactic acid produced by biological fermentation, which can be converted into water and carbon dioxide under appropriate temperature, humidity and microbial conditions, without causing environmental pollution, and is recognized as an environmentally safe material. However, due to its high glass transition temperature (about 35-55℃), high melt viscosity and low strength, polylactic acid is less directly applied to the production line of laminated film. Disposable plastic products have brought a great burden to the environment, especially the paper cups, paper bowls and other disposable paper / plastic products we commonly see. In order to protect the environment, it is imperative to use biodegradable materials to make paper cups, paper bowls and other disposable paper / plastic products. Currently, there are two main methods for preparing biodegradable laminated film, method one is to use modified polylactic acid material, and method two is to directly use polylactic acid material for laminating. Generally, method one uses a blend, which on the one hand makes the formula complex, and on the other hand, the addition of additives and the second component of the blend may cause biotoxicity and non-biodegradability; in method two, although there is no problem of incomplete degradation, the necking phenomenon is serious in the processing process, and the laminated layer is not uniform and has a relatively thick thickness under the condition of a laminating speed greater than 50 m / min, which greatly increases the production cost and is not conducive to industrial production. SUMMARY

[0003] The present application aims to at least solve one of the technical problems existing in the prior art, and provide a process and device for extrusion coating of low melt strength plastic, which can improve the coating speed of laminated paper with polylactic acid and other low melt strength plastics as the coating layer, thereby reducing the production cost.

[0004] The present application is achieved by the following technical solutions:

[0005] The first aspect of the present application is to provide a process for extrusion coating of low melt strength plastic, comprising the following steps: step one, extrusion step, extruding the coating layer from the die head of the extruder; step two, heat preservation step, the coating layer extends through the flat die lip extension channel; step three, lamination step, the coating layer is compounded with the substrate in the lamination area.

[0006] Beneficial effects: compared with the prior art, the process for extrusion coating of low melt strength plastic of the present application makes the coating layer pass through the die lip extension channel into the lamination area, so that the coating layer extruded from the die head can continue to maintain a temperature comparable to the die lip port, and the shape memory effect does not occur during stretching, avoiding the problems of uneven stretching and residual stress, which is beneficial to improve the processing speed and the bonding strength of the paper / laminated layer.

[0007] In addition, the flat extension channel of the die lip is closer to the coating layer, so that the heat source is closer to the coating layer, the heating efficiency is improved, and the heat loss is reduced.

[0008] The extension channel of the die lip slows down the cooling rate of the melt, so that the melt can contact the paper base material at a higher temperature, i.e., at a lower viscosity, which facilitates the penetration of the melt into the fibers of the paper base material, thereby enhancing the bonding strength between the coating layer and the paper base material, and further reducing the thickness of the coating layer. Furthermore, the processing speed of the coated paper with a low-melt-strength plastic such as polylactic acid as the coating layer is improved, and the thickness of the coating layer is reduced.

[0009] According to the process for extrusion coating of low-melt-strength plastic according to the first aspect of the present application, the temperature of the extension channel of the die lip is 150-230°C.

[0010] Beneficially, the process for extrusion coating of low-melt-strength plastic according to the present application controls the extension channel of the die lip so that the temperature of the coating layer changes slightly in the range from the die lip opening to the bonding area, thereby avoiding rapid cooling of the coating layer and improving the processing speed and bonding strength, and reducing the thickness of the coating layer within a certain range.

[0011] According to the process for extrusion coating of low-melt-strength plastic according to the first aspect of the present application, one end of the extension channel of the die lip is closed by the die head.

[0012] Beneficially, the process for extrusion coating of low-melt-strength plastic according to the present application controls the extension channel of the die lip so that the temperature of the coating layer changes slightly in the range from the die lip opening to the bonding area, thereby avoiding rapid cooling of the coating layer and improving the processing speed and bonding strength, and reducing the thickness of the coating layer within a certain range.

[0013] According to the process for extrusion coating of low-melt-strength plastic according to the first aspect of the present application, the length of the extension channel of the die lip is 40-100 mm.

[0014] Beneficially, the process for extrusion coating of low-melt-strength plastic according to the present application controls the extension channel of the die lip so that the temperature of the coating layer changes slightly in the range from the die lip opening to the bonding area, thereby avoiding rapid cooling of the coating layer and improving the processing speed and bonding strength, and reducing the thickness of the coating layer within a certain range.

[0015] According to the process for extrusion coating of low-melt-strength plastic according to the first aspect of the present application, the width of the extension channel of the die lip is 10-20 mm.

[0016] Beneficially, the process for extrusion coating of low melt strength plastics of the present application reduces heat loss by defining the width of the die lip extension channel, thereby bringing the heat source closer to the coating layer, and reducing the energy consumption for maintaining the coating layer.

[0017] In addition, defining the width of the die lip extension channel also helps to extend the length of the die lip extension channel, further reducing the exposed length of the coating layer.

[0018] According to the process for extrusion coating of low melt strength plastics of the first aspect of the present application, the shortest distance between the die lip extension channel and the bonding area is 90-150 mm.

[0019] Beneficially, the process for extrusion coating of low melt strength plastics of the present application defines the shortest distance between the die lip extension channel and the bonding area, thereby also ensuring that the die lip extension channel can maintain a safe distance from the bonding area, ensuring minimal exposure of the coating layer and avoiding damage to the substrate caused by the die lip extension channel.

[0020] The second aspect of the present application provides a device for extrusion coating of plastics, comprising a die lip extension device for continuously maintaining the temperature of the film melt, the die lip extension device being installed on the die head.

[0021] Beneficial effect: compared with the prior art, the device for extrusion coating of plastics of the present application installs the die lip extension device on the die head, thereby ensuring that the coating layer can directly enter the die lip extension channel after extrusion, reducing cooling, and also facilitating the adjustment of the positions of the die head and the die lip extension device, so that the die lip extension channel is as close as possible to the bonding area, reducing the exposure of the coating layer, and further reducing the cooling of the coating layer.

[0022] According to the device for extrusion coating of plastics of the second aspect of the present application, the die lip extension device comprises a first side wall, a heater is arranged in the first side wall, the first side wall is arranged in the width direction of the die lip extension channel, and the first side wall is hinged to the die head.

[0023] Beneficial effect: the device for extrusion coating of plastics of the present application hingedly arranges the first side wall to the die head, and arranges the first side wall in the width direction of the die lip extension channel, thereby meeting the need for heat preservation, and also facilitating the cleaning and repair of the die head by turning over the first side wall.

[0024] In the present application, the width direction of the die lip extension channel can also refer to the thickness direction of the coating layer.

[0025] According to the second aspect of the present application, the free end of the first side wall is provided with an inclined angle, which is arranged on the side of the first side wall away from the die lip extension channel.

[0026] Beneficial effects: the device for plastic extrusion coating of the present application can reduce the minimum distance between the die lip extension channel and the fitting area through the inclined angle, thereby facilitating adjustment and making the die lip extension channel closer to the fitting area, so as to further reduce the exposure of the coating layer.

[0027] According to the second aspect of the present application, the die lip extension channel comprises a second side wall, which is arranged adjacent to the first side wall and is fixedly connected with the die head.

[0028] Beneficial effects: the device for plastic extrusion coating of the present application can reduce heat loss of the die lip extension channel and improve the heat preservation effect by arranging the second side wall, so that the first side wall and the second side wall cooperate to form the die lip extension channel. BRIEF DESCRIPTION OF DRAWINGS

[0029] The present application will be further described below in combination with the drawings and examples.

[0030] Figure 1 The present application will be further described below in combination with the drawings and examples.

[0031] Figure 2 The present application will be further described below in combination with the drawings and examples. Figure 1 The present application will be further described below in combination with the drawings and examples.

[0032] REFERENCE SIGNS

[0033] 100 - die head

[0034] 200 - die lip extension channel, 210 - die lip extension device, 211 - first side wall, 212 - second side wall, 213 - inclined plate

[0035] 300 - fitting area, 310 - fitting device, 311 - first roller, 312 - second roller DETAILED DESCRIPTION

[0036] This part will describe the specific embodiments of the present application in detail, and the preferred embodiments of the present application are shown in the drawings, which serve to supplement the description in the text part of the specification and enable people to intuitively and visually understand each technical feature and the overall technical scheme of the present application, but it cannot be understood as a limitation on the protection scope of the present application.

[0037] In the description of the present application, it should be understood that the orientation description, such as the orientation or position relationship indicated by up, down, front, back, left, right and the like, is based on the orientation or position relationship shown in the drawings, and is only for the convenience of describing the present application and simplifying the description, and does not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application.

[0038] In the description of the present application, one or more is understood as one or more, more than two is understood as more than two, greater than, less than, more than, etc. are understood as not including the number, above, below, within, etc. are understood as including the number. If the first, second is described, it is only for the purpose of distinguishing technical features, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of indicated technical features or the sequence of indicated technical features.

[0039] In the description of the present application, unless otherwise explicitly limited, the words such as setting, installing, connecting, etc. should be broadly understood, and those skilled in the art can reasonably determine the specific meaning of the above words in the present application in combination with the specific content of the technical solution.

[0040] Referring to Figure 1 , an apparatus for plastic extrusion coating is provided, which is particularly suitable for the composite extrusion of a coating layer made of polylactic acid.

[0041] In terms of structure, from top to bottom, there are a die head 100, a die lip extension device 210 and a fitting device 310.

[0042] The die head 100 is used to extrude the heated and melted polylactic acid into a film shape.

[0043] The die head 100 is generally assembled by left and right half dies, so that a narrow and long gap is formed at the bottom of the die head 100, and thus the polylactic acid is extruded into a film shape.

[0044] For the die lip extension device 210, refer to Figure 1 and Figure 2 The heat preservation device 210 is fixed on the die head.

[0045] In terms of structure, the die lip extension device 210 has a bevel plate 213 fitted with the die head 100, and a bolt is installed on the bevel plate 213 to realize the fixation of the bevel plate 213 and the die head 100.

[0046] In terms of structure, the die lip extension device 210 also has a first side wall 211 and a second side wall 212, both of which are two, forming a die lip extension channel 200 with a rectangular cross section.

[0047] Since the width of the coating layer is usually several meters, and the thickness of the coating layer is less than one millimeter, the cross section of the lip extension passage 200 is also narrow and long.

[0048] The first side wall 211 is arranged in the width direction of the lip extension passage 200, and a heater is arranged in the first side wall 211.

[0049] The first side wall 211 is arranged in the width direction of the lip extension passage 200, that is, the first side wall 211 is arranged in the thickness direction of the coating layer, so that the distance between the heater and the coating layer can be reduced, the coating layer can be efficiently heated, and the shape memory effect caused by uneven stretching and crystallization due to temperature reduction can be avoided.

[0050] In addition, the first side wall 211 is hinged to the die head 100, so that when the die head 100 needs to be maintained, the first side wall 211 can be flipped over, thereby facilitating cleaning and repair of the die head 100.

[0051] Correspondingly, the second side wall 212 is arranged adjacent to the first side wall 211, so that the first side wall 211 and the second side wall 212 cooperate to form a ring-shaped closed lip extension passage 200, thereby reducing heat loss of the lip extension passage 200 and improving heat preservation effect.

[0052] The bonding device 310 mainly includes two pressure rollers, one of which is used to drive the substrate to move, and the other of which is used to press the coating layer to the substrate to realize the combination of the coating layer and the substrate.

[0053] As shown, the coating layer is extruded from top to bottom, and the coating layer moves vertically downward, thereby reducing the risk of the coating layer contacting the heat preservation device 210. Of course, the coating layer can also directly descend to the area where the two pressure rollers are extruded.

[0054] The two pressure rollers of the bonding device 310 also form a bonding area 300, which includes the part where the two pressure rollers are extruded, and the surface of the two pressure rollers close to the heat preservation device 210. Of course, this refers to the spatial position, not the specific position of the surface of the pressure roller.

[0055] As shown, the free end of the first side wall 211 is provided with an inclined angle, and the inclined angle is arranged on the side of the first side wall 211 away from the lip extension passage 200.

[0056] The inclined angle can increase the minimum distance between the lip extension device 210 and the bonding area 300, thereby facilitating adjustment and making the heat preservation device 210 closer to the bonding area 300, so as to further reduce the exposure of the coating layer.

[0057] Correspondingly, the device for low melt strength plastic extrusion coating of the embodiment corresponds to a process for low melt strength plastic extrusion coating, and the process for low melt strength plastic extrusion coating comprises the following steps:

[0058] Step one, an extrusion step, extruding the coating layer from the die head 100 of the extruder;

[0059] Step two, a heat preservation step, the coating layer extends through the flat die lip extension channel 200;

[0060] Step three, a lamination step, the coating layer is compounded with the substrate in the lamination area 300.

[0061] In the embodiment, the coating layer enters the lamination area 300 via the die lip extension channel 200, so that the coating layer extruded from the die head 100 is heated, avoiding the temperature of the coating layer from decreasing too fast and avoiding the coating layer from hardening.

[0062] Since the die lip extension channel slows down the temperature decreasing rate of the film melt, the film melt can contact the paper substrate at a higher temperature, i.e., at a lower viscosity, which is beneficial to the penetration of the melt into the fibers of the paper substrate, thereby enhancing the bonding strength between the film layer and the paper substrate, and further reducing the thickness of the film layer.

[0063] In addition, the die lip extension channel 200 is flat, so that the heat source on the die lip extension channel 200 is closer to the coating layer, improving the heating efficiency and reducing heat loss.

[0064] In some preferred embodiments, the temperature of the die lip extension channel 200 can be 180-220°C.

[0065] The embodiment controls the temperature of the die lip extension channel 200 to make the temperature of the coating layer change in a small range, thereby avoiding the temperature decreasing rate of the coating layer from being too fast and avoiding the memory effect caused by melt stretching.

[0066] In some preferred embodiments, one end of the die lip extension channel 200 can be closed by the die head 100.

[0067] The embodiment closes one end of the die lip extension channel 200 by the die head 100, so that the coating layer directly enters the die lip extension channel 200 after being extruded, avoiding the coating layer from being cooled and avoiding the temperature of the coating layer from decreasing too early.

[0068] In some preferred embodiments, the length of the die lip extension channel 200 can be 40-100 mm.

[0069] The embodiment sets the length of the lip extension channel 200 reasonably, thereby reducing the exposure of the coating layer, making the coating layer enter the bonding area 300 after a short distance after passing through the lip extension channel 200, and quickly performing compounding to avoid defects caused by temperature drop of the coating layer.

[0070] In some preferred schemes, the width of the lip extension channel 200 can be 10-20 mm.

[0071] The embodiment limits the width of the lip extension channel 200, thereby making the heat source closer to the coating layer, reducing heat loss, and thereby reducing the energy consumption for heat preservation of the coating layer.

[0072] In addition, limiting the width of the lip extension channel 200 is also beneficial to extending the length of the lip extension channel 200 and further reducing the exposure of the coating layer.

[0073] In some preferred schemes, the shortest distance between the lip extension channel 200 and the bonding area 300 can be 90-150 mm.

[0074] The shortest distance between the lip extension channel 200 and the bonding area 300 can also ensure that the lip extension device 210 forming the lip extension channel 200 can maintain a safe distance from the bonding area 300, thereby ensuring minimal exposure of the coating layer and avoiding damage to the substrate caused by the lip extension device 210.

[0075] In addition, on the equipment for low melt strength plastic extrusion coating, by installing the lip extension device 210 forming the lip extension channel 200 on the die head 100, the coating layer can be directly extruded into the lip extension channel 200 after extrusion, reducing cooling, and also facilitating adjustment of the positions of the die head 100 and the lip extension device 210, so that the lip extension device 210 is as close as possible to the bonding area 300, reducing the exposure of the coating layer and further reducing the cooling of the coating layer.

[0076] The equipment for low melt strength plastic extrusion coating and the process for low melt strength plastic extrusion coating of the embodiment are mainly for polylactic acid.

[0077] The melting point of polylactic acid is 153-158°C, the decomposition temperature is 230°C, and the temperature range at which polylactic acid remains liquid is 153-230°C.

[0078] When the embodiment is applied, the following comparisons can be made.

[0079]

[0080] From the above table, after the application of the embodiment, the lamination process of polylactic acid is greatly improved, the application is convenient, and the effect of protecting the environment is improved.

[0081] The embodiments of the present application are described in detail above with reference to the drawings, but the present application is not limited to the above embodiments, and various changes can be made within the knowledge of those skilled in the art without departing from the spirit of the present application.

Claims

1. A process for low melt strength plastic extrusion coating, characterized by, The process is realized by an equipment for plastic extrusion coating, which comprises a die head and a die lip extension device for forming a die lip extension channel, one end of the die lip extension channel being closed by the die head, the die lip extension device being mounted on the die head, the die lip extension device comprising a first side wall, a heater being arranged in the first side wall, the temperature of the die lip extension channel being 150-230 DEG C, the length of the die lip extension channel being 40-100 mm, the width of the die lip extension channel being 10-20 mm, the first side wall being arranged in the width direction of the die lip extension channel, the first side wall being hinged to the die head, the free end of the first side wall being provided with an oblique angle, the oblique angle being arranged on the side of the first side wall away from the die lip extension channel, the shortest distance between the die lip extension channel and the bonding area being 90-150 mm, the die lip extension channel being of a flat structure, the die lip extension device comprising a second side wall, the second side wall being arranged adjacent to the first side wall, the second side wall being fixedly connected to the die head; The process comprises the following steps: Step one, extrusion step, extruding a coating layer from the die head of an extruder; Step two, heat preservation step, the coating layer passing through the flat die lip extension channel; Step three, the lamination step, the coating layer is compounded with the substrate in the lamination area, the processing speed of the polylactic acid coating layer is increased to more than 50 m / min, and the thickness is reduced to 30 g / m 2 The following.

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