A multi-layer co-extrusion molding method of a composite film material for building

Abstract

The present application relates to the technical field of co-extrusion molding, and particularly relates to a multilayer co-extrusion molding method of a composite membrane material for building, comprising the following steps: synchronously co-extruding high polymer mixtures of each layer after melting and plasticizing to obtain a composite tubular melt blank; injecting gas into the composite tubular melt blank and pulling to obtain a composite tubular film bubble; determining whether the preparation of the composite tubular film bubble is up to standard according to a film bubble form characterization value; cooling and solidifying the composite tubular film bubble up to standard to obtain a composite tubular film; when the preparation of the composite tubular film is not up to standard according to a circumferential cooling uniformity characterization value, determining an adjustment strategy when the preparation of the composite tubular film is not up to standard according to a circumferential wind speed extreme value ratio of a cooling air ring; and obtaining the composite membrane material for building after clamping and winding the composite tubular film up to standard. The present application improves the co-extrusion molding efficiency of the composite membrane material for building.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of co-extrusion molding, in particular to a multi-layer co-extrusion molding method of a composite film material for building. BACKGROUND

[0002] Co-extrusion composite refers to the production of polymer film by multi-layer co-extrusion process, which has excellent barrier properties, mechanical properties, forming properties and heat sealing properties. The processing does not need additional glue composite process, and does not involve the residual problem of solvents such as ink, adhesive and additive, so the application range of co-extrusion composite process is becoming more and more extensive.

[0003] The composite film material for building is a new type of enclosure material, which is widely used in inflatable film venues, temporary building enclosure, building waterproof and impermeable layer, energy-saving and environment-friendly greenhouse, outdoor public facility sunshade and other scenes due to its light weight, convenient construction, large span and strong weather resistance. This kind of film material needs to meet the core requirements of long-term outdoor weather resistance, stable mechanical structure, sealing and impermeability, splicing and other requirements, and the co-extrusion composite process can precisely match the above requirements through the characteristics of multi-layer function integration.

[0004] However, the use environment of the composite film material for building is much harsher than that of the packaging film, which puts forward requirements far beyond ordinary film on the dimensional stability, circumferential uniformity and process controllability of the product.

[0005] Chinese patent application publication No. CN109732892A discloses a manufacturing method and equipment of a multi-layer thermal insulation plastic inflatable film. The equipment mainly comprises a multi-layer co-extrusion blow molding die, which is composed of an outer die ring, an inner die ring and a plurality of intermediate die rings between the inner and outer die rings. The air flow of the air blower is sprayed through the air inlet of the intermediate die ring and the air outlet of the center part in the hollow part of each die ring. Each blow molding machine melts the plastic polymer particles in the hopper bin into liquid state, and then extrudes the molten liquid into the corresponding feeding port of each die ring. The air flow sprayed from the air outlet of the center part in the hollow part of each die ring divides the liquid flowing out of the film outlet into a cavity and separates from the surface of the heated multi-layer co-extrusion blow molding die.

[0006] However, the present technology still has the following problems: the film bubble shape in the film blowing process and the uniformity of the tubular film circumferential cooling process have not been considered, which affects the thickness and size of the building film material, resulting in poor co-extrusion molding efficiency of the composite film material for building. SUMMARY

[0007] To this end, the present application provides a multi-layer co-extrusion molding method of a composite building film material to overcome the problem of poor co-extrusion molding efficiency of the composite building film material caused by the fact that the existing technology does not consider the influence of the bubble shape in the film blowing process and the uniformity of the circumferential cooling process of the tubular film on the thickness and size of the building film material.

[0008] To achieve the above-mentioned object, the present application provides a multi-layer co-extrusion molding method of a composite building film material, comprising:

[0009] The high polymer mixtures of the layers are respectively placed in independent extruders, melted and plasticized at a preset maximum melting temperature difference, and then introduced into a co-extrusion die of a co-extrusion film blowing machine for synchronous co-extrusion at a preset processing temperature to obtain a composite tubular melt blank.

[0010] Air is injected into the interior of the composite tubular melt blank at a preset inflation pressure, and the composite tubular melt blank is pulled at a preset pulling rate to obtain a composite tubular film bubble.

[0011] Based on the contour pixel area of the image of the composite tubular film bubble, a bubble shape stability characteristic value is obtained, and whether the preparation of the composite tubular film bubble meets the preset standard is determined according to the bubble shape characteristic value.

[0012] The composite tubular film bubble meeting the preset standard is cooled and solidified by a cooling air ring to obtain a composite tubular film, and a circumferential cooling uniformity characteristic value is obtained based on the circumferential temperature of the composite tubular film before and after cooling and solidification.

[0013] When it is determined according to the circumferential cooling uniformity characteristic value that there is a risk that the preparation of the composite tubular film does not meet the preset standard, whether the preparation of the composite tubular film meets the preset standard is determined again according to the diameter fluctuation variance of the composite tubular film.

[0014] When it is determined according to the circumferential cooling uniformity characteristic value that the preparation of the composite tubular film does not meet the preset standard, an adjustment strategy for the preparation of the composite tubular film that does not meet the preset standard is determined according to the circumferential air speed extreme value ratio of the cooling air ring, wherein the adjustment strategy is to reduce the preset processing temperature or to reduce the air volume of the air outlet corresponding to the maximum air speed of the cooling air ring.

[0015] The composite tubular film meeting the preset standard is clamped and wound to obtain a composite building film material.

[0016] Further, the high polymer mixtures of the layers are respectively a mixture of linear low-density polyethylene, an antioxidant and an ultraviolet absorber for the outer layer; a mixture of linear low-density polyethylene, a polyolefin elastomer, an ethylene-butyl acrylate copolymer and a reinforcing filler for the middle layer; and a mixture of linear low-density polyethylene and an ethylene-butyl acrylate copolymer for the inner layer.

[0017] Further, the process of determining whether the preparation of the composite tubular film bubble meets the preset standard according to the film bubble morphology characterization value of the composite tubular film bubble comprises:

[0018] Comparing the film bubble morphology characterization value with a first preset film bubble morphology characterization value and a second preset film bubble morphology characterization value respectively;

[0019] If the film bubble morphology characterization value is less than the first preset film bubble morphology characterization value, it is determined that the preparation of the composite tubular film bubble meets the preset standard;

[0020] If the film bubble morphology characterization value is greater than or equal to the first preset film bubble morphology characterization value and less than the second preset film bubble morphology characterization value, it is determined that the preparation of the composite tubular film bubble does not meet the preset standard, and the preset inflation pressure is increased according to the difference between the film bubble morphology characterization value and the first preset film bubble morphology characterization value;

[0021] If the film bubble morphology characterization value is greater than or equal to the second preset film bubble morphology characterization value, it is determined that the preparation of the composite tubular film bubble does not meet the preset standard and the preset maximum melt temperature difference is reduced according to the difference between the film bubble morphology characterization value and the second preset film bubble morphology characterization value.

[0022] Further, the process of obtaining the film bubble morphology stability characterization value comprises:

[0023] Taking a plurality of front projection images of the composite tubular film bubble at a preset frequency within a first preset time period;

[0024] Extracting the pixel area surrounded by the contour of the composite tubular film bubble in each image;

[0025] Calculating the standard deviation of all pixel areas, denoted as the film bubble morphology stability characterization value.

[0026] Further, there are a plurality of temperature difference adjustment modes for the reduction of the preset maximum melt temperature difference, and each temperature difference adjustment mode has a different reduction amplitude of the preset maximum melt temperature difference.

[0027] Further, the process of determining whether the preparation of the composite tubular film meets the preset standard according to the circumferential cooling uniformity characterization value of the composite tubular film comprises:

[0028] Comparing the circumferential cooling uniformity characterization value with a first preset circumferential cooling uniformity characterization value and a second preset circumferential cooling uniformity characterization value respectively;

[0029] If the circumferential cooling uniformity characterization value is less than the first preset circumferential cooling uniformity characterization value, it is determined that the preparation of the composite tubular film meets the preset standard;

[0030] if the circumferential cooling uniformity value is greater than or equal to a first preset circumferential cooling uniformity value and less than a second preset circumferential cooling uniformity value, it is determined that the preparation of the composite tubular film does not meet the preset standard, and the adjustment strategy when the preparation of the composite tubular film does not meet the preset standard is determined according to the circumferential wind speed extreme value ratio of the cooling air ring.

[0031] if the circumferential cooling uniformity value is greater than or equal to a second preset circumferential cooling uniformity value, it is determined that the preparation of the composite tubular film does not meet the preset standard, and the adjustment strategy when the preparation of the composite tubular film does not meet the preset standard is determined according to the circumferential wind speed extreme value ratio of the cooling air ring.

[0032] Further, the process of obtaining the circumferential cooling uniformity value comprises:

[0033] Before cooling and solidification, the temperatures of a plurality of circumferentially arranged monitoring points of the composite tubular film to be cooled are collected;

[0034] After cooling and solidification, the temperatures of the monitoring points are collected;

[0035] The difference between the temperature before cooling and the temperature after cooling of each monitoring point is calculated, which is recorded as the cooling temperature difference of each monitoring point;

[0036] The standard deviation of all cooling temperature differences is recorded as the circumferential cooling uniformity value.

[0037] Further, according to the secondary determination result of the comparison between the diameter fluctuation variance of the composite tubular film and the preset diameter fluctuation variance, when the preparation of the composite tubular film does not meet the preset standard, the preset pulling rate is reduced according to the ratio of the diameter fluctuation variance to the preset fluctuation variance.

[0038] Further, the process of obtaining the diameter fluctuation variance of the composite tubular film comprises:

[0039] After the cooling and solidification of the composite tubular film, the diameters of a plurality of the composite tubular films are collected within a second preset time period at a preset collection frequency;

[0040] The variance of all diameters is calculated, which is the diameter fluctuation variance of the composite tubular film.

[0041] Further, the adjustment strategy when the preparation of the composite tubular film does not meet the preset standard according to the wind speed extreme value ratio of the cooling air ring comprises:

[0042] if the wind speed extreme value ratio is less than a preset wind speed extreme value ratio, the preset processing temperature of the co-extrusion die is reduced according to the difference between the preset wind speed extreme value ratio and the wind speed extreme value ratio;

[0043] If the wind speed extreme value ratio is greater than or equal to the preset wind speed extreme value ratio, the air volume of the air outlet corresponding to the maximum wind speed of the cooling air ring is reduced according to the difference between the wind speed extreme value ratio and the preset wind speed extreme value ratio.

[0044] The wind speed extreme value ratio of the cooling air ring is the ratio of the maximum wind speed to the minimum wind speed in each air outlet of the cooling air ring.

[0045] Compared with the prior art, the beneficial effects of the present application are that the present application solves the problem of insufficient outdoor weather resistance of the building film by setting the outer layer added with antioxidants and ultraviolet absorbers, the introduction of the polyolefin elastomer and the reinforcing filler in the middle layer improves the mechanical bearing capacity of the film, the ethylene-butyl acrylate copolymer in the inner layer optimizes the heat sealing splicing performance, and the linear low density polyethylene as the base material ensures the interlayer compatibility; by monitoring the film bubble shape and the cooling uniformity of the tubular film, the thickness uniformity and dimensional stability of the film are ensured, and the mechanical properties of the obtained building film are reliable; by introducing the film bubble shape characterization value and the circumferential cooling uniformity characterization value, intelligent monitoring of the production process is realized, thereby improving the co-extrusion molding efficiency of the building composite film.

[0046] Further, the present application compares the film bubble shape characterization value with two preset threshold values respectively, differentiates the film bubble instability problem, adjusts the blow-up pressure for slight fluctuations, and adjusts the melt temperature difference for serious fluctuations, so that the process correction is fast and accurate, thereby improving the preparation stability.

[0047] Further, the present application constructs a three-level monitoring mechanism of cooling quality based on the circumferential cooling uniformity characterization value, in the risk warning state of not meeting the standard, the system does not directly make the final adjustment, but makes a secondary determination through the diameter fluctuation variance to avoid misjudgment; for the substandard state, the adjustment strategy is determined in combination with the circumferential wind speed extreme ratio of the cooling air ring to ensure the uniformity of the film material circumferential size, thereby improving the reliability of the determination.

[0048] Further, the present application reduces the pulling rate when the preparation of the composite tubular film is not up to standard in the cooling uniformity warning and the diameter fluctuation variance secondary determination, reduces the overall tensile strain in the film material preparation process, and reserves more sufficient time for tubular film cooling and shaping, thereby ensuring the uniformity of the film material circumferential size.

[0049] Further, the present application directly judges the uniformity of the circumferential air supply of the cooling air ring through the wind speed extreme value ratio, the greater the wind speed extreme value ratio, the greater the circumferential wind speed difference, and the more prominent the uneven cooling problem, thereby realizing accurate positioning of the root cause of uneven cooling. BRIEF DESCRIPTION OF DRAWINGS

[0050] Figure 1Flow chart of the multilayer co-extrusion molding method of the building composite film material according to the embodiment of the present application;

[0051] Figure 2 Flow chart of the method for determining whether the preparation of the composite tubular film bubble meets the preset standard according to the embodiment of the present application;

[0052] Figure 3 Flow chart of the method for determining whether the preparation of the composite tubular film meets the preset standard according to the circumferential cooling uniformity characterization value of the composite tubular film according to the embodiment of the present application;

[0053] Figure 4 Flow chart of the adjustment strategy when the preparation of the composite tubular film does not meet the preset standard according to the embodiment of the present application. DETAILED DESCRIPTION

[0054] In order to make the objects and advantages of the present application clearer, the present application will be further described below in conjunction with embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and not to limit the protection scope of the present application.

[0055] The preferred embodiments of the present application will be described below with reference to the accompanying drawings. Those skilled in the art should understand that these embodiments are only used to explain the technical principles of the present application and not to limit the protection scope of the present application.

[0056] It should be pointed out that the data in the present embodiment are obtained by comprehensive analysis and evaluation of historical detection data and corresponding historical detection results of the present application in the past three months before the present detection. Those skilled in the art can understand that the determination method of the present application for a single parameter can be to select the value with the highest proportion as the preset standard parameter according to the data distribution, to use weighted summation to obtain the value as the preset standard parameter, to substitute each historical data into a specific formula and to obtain the value as the preset standard parameter using the formula, or other selection methods, as long as the present application can clearly define different specific situations in the single determination process through the obtained value.

[0057] Please refer to Figure 1 , Figure 2 , Figure 3 and Figure 4 , which are respectively flow chart of the multilayer co-extrusion molding method of the building composite film material according to the embodiment of the present application; flow chart of the method for determining whether the preparation of the composite tubular film bubble meets the preset standard according to the embodiment of the present application; flow chart of the method for determining whether the preparation of the composite tubular film meets the preset standard according to the circumferential cooling uniformity characterization value of the composite tubular film according to the embodiment of the present application; and flow chart of the adjustment strategy when the preparation of the composite tubular film does not meet the preset standard according to the embodiment of the present application.

[0058] The multi-layer co-extrusion molding method of the building composite film material comprises the following steps:

[0059] In step S1, the polymer mixtures of the layers are respectively placed in independent extruders, melted and plasticized with a preset maximum melting temperature difference of 10 DEG C, and then introduced into a co-extrusion die of a co-extrusion film blowing machine to be synchronously co-extruded at a preset processing temperature of 200 DEG C, so as to obtain a composite tubular melt blank, wherein the composite tubular melt blank is a vertically downward hollow thin-walled cylindrical melt extruded from the co-extrusion die, and the melt of each layer is integrated in the die.

[0060] In step S2, gas is injected into the inside of the composite tubular melt blank at a preset blowing pressure of 0.02 MPa, and the composite tubular melt blank is pulled at a preset pulling speed of 8 m / min by a pulling roller, so as to obtain a composite tubular bubble;

[0061] In step S3, a bubble shape stability characteristic value is obtained based on the contour pixel area of the image of the composite tubular bubble, and whether the preparation of the composite tubular bubble meets the preset standard is determined according to the bubble shape characteristic value;

[0062] In step S4, the composite tubular bubble meeting the preset standard is cooled and solidified by a cooling air ring to obtain a composite tubular film, and a circumferential cooling uniformity characteristic value is obtained based on the circumferential temperature of the composite tubular film before and after cooling and solidification;

[0063] In step S5, when it is determined according to the circumferential cooling uniformity characteristic value that the preparation of the composite tubular film has a risk of not meeting the preset standard, whether the preparation of the composite tubular film meets the preset standard is determined according to the diameter fluctuation variance of the composite tubular film;

[0064] In step S6, when it is determined according to the circumferential cooling uniformity characteristic value that the preparation of the composite tubular film does not meet the preset standard, an adjustment strategy for the preparation of the composite tubular film when it does not meet the preset standard is determined according to the circumferential wind speed extreme value ratio of the cooling air ring, wherein the adjustment strategy is to reduce the preset processing temperature or to reduce the air volume of the air outlet corresponding to the maximum wind speed of the cooling air ring;

[0065] In step S7, the composite tubular film meeting the preset standard is clamped by a herringbone plate, and then wound by a winding machine to obtain a building composite film material.

[0066] Specifically, the three polymer mixtures for the respective layers are as follows: a mixture of 93 parts by weight of linear low density polyethylene, 5 parts by weight of antioxidant and 2 parts by weight of ultraviolet light absorber for the outer layer; a mixture of 80 parts by weight of linear low density polyethylene, 10 parts by weight of polyolefin elastomer, 8 parts by weight of ethylene-butyl acrylate copolymer and 2 parts by weight of reinforcing filler for the middle layer; a mixture of 70 parts by weight of linear low density polyethylene and 30 parts by weight of ethylene-butyl acrylate copolymer for the inner layer. In this embodiment, the antioxidant is Irganox 1010 from BASF, the ultraviolet light absorber is UV-531, the polyolefin elastomer is ethylene-octene copolymer, the ethylene-butyl acrylate copolymer contains 25-35 wt% of butyl acrylate monomer, and the reinforcing filler is 2000-mesh talc.

[0067] In this embodiment, the outer layer is a weather-resistant layer with a thickness of 0.08 mm, the middle layer is a reinforcing layer with a thickness of 0.12 mm, and the inner layer is an adhesive layer with a thickness of 0.05 mm.

[0068] Specifically, the three polymer mixtures are respectively fed into three independent single-screw extruders, the melt temperature of the outer layer extruder is 195°C, the melt temperature of the middle layer extruder is 200°C, and the melt temperature of the inner layer extruder is 190°C.

[0069] Specifically, the process of determining whether the preparation of the composite tubular film bubble meets the preset standard according to the film bubble morphology characterization value of the composite tubular film bubble includes:

[0070] The film bubble morphology characterization value is compared with a first preset film bubble morphology characterization value 0.020 and a second preset film bubble morphology characterization value 0.050, respectively;

[0071] If the film bubble morphology characterization value is less than the first preset film bubble morphology characterization value, it is determined that the preparation of the composite tubular film bubble meets the preset standard;

[0072] If the film bubble morphology characterization value is greater than or equal to the first preset film bubble morphology characterization value and less than the second preset film bubble morphology characterization value, it is determined that the preparation of the composite tubular film bubble does not meet the preset standard, and the preset inflation pressure is increased according to the difference between the film bubble morphology characterization value and the first preset film bubble morphology characterization value;

[0073] If the film bubble morphology characterization value is greater than or equal to the second preset film bubble morphology characterization value, it is determined that the preparation of the composite tubular film bubble does not meet the preset standard, and the preset maximum melt temperature difference is decreased according to the difference between the film bubble morphology characterization value and the second preset film bubble morphology characterization value.

[0074] Specifically, the first preset bubble morphology characteristic value is in the range of [0.010, 0.025], and the second preset bubble morphology characteristic value is in the range of [0.045, 0.060]. Preferably, the first preset bubble morphology characteristic value is 0.020, and the second preset bubble morphology characteristic value is 0.050. However, the above values are not limited thereto, and those skilled in the art can adjust the above values according to actual needs.

[0075] Specifically, the smaller the bubble morphology characteristic value, the closer the size of the bubble at each instant to the reference value, that is, the more stable the morphology; the larger the bubble morphology characteristic value, the more intense the bubble shaking, swinging or periodic expansion or contraction, and the more unstable the morphology; for the bubble morphology characteristic value between the two thresholds, the blowing pressure directly determines the bubble expansion degree and morphology retention, and fine tuning can quickly correct the area fluctuation, so the strategy of increasing the blowing pressure is adopted; for the bubble morphology characteristic value greater than or equal to the second preset value, the root cause is that the large melt temperature difference between the layers leads to viscosity mismatch, which in turn causes uneven stress and morphology out of control during bubble blowing. By reducing the preset maximum melt temperature difference, the melt flow adaptability is optimized from the source of plasticization.

[0076] Specifically, the bubble morphology stability characteristic value acquisition process includes:

[0077] A plurality of orthographic projection images of the composite tubular bubble are captured using an industrial line array scanning camera at a preset frequency of 5 Hz within a first preset time length of 30 s, wherein the collection range of the orthographic projection images is a vertical space region of the composite tubular bubble from the die lip plane of the lower edge of the co-extrusion die to the inlet plane of the cooling air ring; the vertical space region covers the complete free blowing zone from extrusion, blowing, to entering the forced cooling, and is the region where the bubble morphology is most active and most susceptible to process parameters;

[0078] Each bubble orthographic projection image collected is subjected to Gaussian filtering by OpenCV library to suppress noise, and a smoothed image is output. An adaptive threshold segmentation algorithm is used to process the smoothed image, dynamically separate the bubble and the background, and output a binary image. A contour finding algorithm (such as cv2.findContours) is used to retrieve the outer contour in the binary image, and the main contour point sequence with the largest area and located in the central region of the image is extracted as the output, to obtain the contour point sequence of the outermost contour of the bubble. The contour point sequence is input into a contour area calculation function (such as cv2.contourArea), and the pixel area surrounded by the outermost contour of the bubble is calculated according to Green's formula. The image processing method based on OpenCV library is a conventional technical means for those skilled in the art to realize the conversion from image to quantitative data;

[0079] The standard deviation of all pixel areas is calculated and recorded as the bubble morphology stability characteristic value.

[0080] Specifically, several temperature difference adjustment modes are provided for the reduction of the preset maximum melting temperature difference, wherein,

[0081] If the film bubble shape difference value is less than the first preset film bubble shape difference value 0.035, the preset maximum melting temperature difference is reduced to a corresponding value by using a first adjustment coefficient 0.97;

[0082] If the film bubble shape difference value is greater than or equal to the first preset film bubble shape difference value and less than the second preset film bubble shape difference value 0.061, the preset maximum melting temperature difference is reduced to a corresponding value by using a second adjustment coefficient 0.95;

[0083] If the film bubble shape difference value is greater than or equal to the second preset film bubble shape difference value, the preset maximum melting temperature difference is reduced to a corresponding value by using a third adjustment coefficient 0.93;

[0084] The film bubble shape difference value is the difference between the film bubble shape characteristic value and the second preset film bubble shape characteristic value.

[0085] Specifically, the process of determining whether the preparation of the composite tubular film meets the preset standard according to the circumferential cooling uniformity characteristic value of the composite tubular film includes:

[0086] The circumferential cooling uniformity characteristic value is compared with a first preset circumferential cooling uniformity characteristic value 2.1℃ and a second preset circumferential cooling uniformity characteristic value 7.1℃, respectively;

[0087] If the circumferential cooling uniformity characteristic value is less than the first preset circumferential cooling uniformity characteristic value, it is determined that the preparation of the composite tubular film meets the preset standard;

[0088] If the circumferential cooling uniformity characteristic value is greater than or equal to the first preset circumferential cooling uniformity characteristic value and less than the second preset circumferential cooling uniformity characteristic value, it is determined that the preparation of the composite tubular film has a risk of not meeting the preset standard, and whether the preparation of the composite tubular film meets the preset standard is further determined according to the diameter fluctuation variance of the composite tubular film;

[0089] If the circumferential cooling uniformity characteristic value is greater than or equal to the second preset circumferential cooling uniformity characteristic value, it is determined that the preparation of the composite tubular film does not meet the preset standard, and the adjustment strategy when the preparation of the composite tubular film does not meet the preset standard is determined according to the circumferential wind speed extreme ratio of the cooling air ring.

[0090] Specifically, the first preset circumferential cooling uniformity characteristic value is in the range of [1.7℃, 3.5℃], and the second preset circumferential cooling uniformity characteristic value is in the range of [6.7℃, 8.5℃]. Preferably, the first preset circumferential cooling uniformity characteristic value is 2.1℃, and the second preset circumferential cooling uniformity characteristic value is 7.1℃. However, the above values are not limited thereto, and those skilled in the art can adjust the above values according to actual needs.

[0091] Specifically, the circumferential cooling uniformity characteristic value reflects the consistency of the cooling rate at each position of the film bubble. The smaller the circumferential cooling uniformity characteristic value, the more uniform the cooling, and the more consistent the thermal shrinkage rate of the film material in the circumferential direction, thereby avoiding misalignment and stress cracking during splicing. On the contrary, the cooling is uneven, which easily leads to size fluctuation of the finished building composite film.

[0092] Specifically, by comparing the circumferential cooling uniformity characteristic value with the first and second preset threshold values, the cooling state corresponding to the circumferential cooling uniformity characteristic value is divided into three categories: meeting the standard, being at risk, and not meeting the standard. When the circumferential cooling uniformity characteristic value is less than the first preset value, the temperature difference of the tubular film in the circumferential direction is extremely small, and the consistency of the thermal shrinkage rate meets the requirements of splicing and long-term use of the building film, thereby directly determining that it is qualified to ensure production efficiency. When the circumferential cooling uniformity characteristic value is greater than or equal to the second preset value, the cooling is uneven, which leads to significant differences in the crystallization state and shrinkage amount of the tubular film, thereby causing size fluctuation and stress concentration, and directly determining that it is unqualified. For the at-risk state of the circumferential cooling uniformity characteristic value between the two threshold values, the diameter fluctuation variance is introduced for secondary verification, thereby realizing the correlation between the cooling process representation and the finished product size result, and effectively avoiding missed judgment.

[0093] Specifically, the process of obtaining the circumferential cooling uniformity characteristic value comprises:

[0094] Eight infrared temperature measurement probes are arranged equidistantly in the circumferential direction at 10cm above the inlet plane and 10cm below the outlet plane of the cooling air ring as monitoring points, thereby forming a temperature measurement array, wherein the optical axis of each infrared temperature measurement probe is vertically aligned with the surface of the composite tubular film and focused on the same measurement distance;

[0095] Before cooling and solidification, the temperatures of the monitoring points arranged in the circumferential direction of the composite tubular film to be cooled are collected;

[0096] After cooling and solidification, the temperatures of the monitoring points are collected;

[0097] The difference between the temperature before cooling and the temperature after cooling of each monitoring point is calculated, which is recorded as the cooling temperature difference of each monitoring point;

[0098] The standard deviation of all cooling temperature differences is recorded as the circumferential cooling uniformity characteristic value. In this embodiment, the infrared temperature measurement probe is preferably a colorimetric infrared temperature measurement instrument.

[0099] Specifically, the preparation of the composite tubular film is determined to meet the preset standard according to the variance of the diameter fluctuation of the composite tubular film, wherein,

[0100] If the variance of the diameter fluctuation is less than a preset variance of the diameter fluctuation 0.0004 mm 2 , it is determined that the preparation of the composite tubular film meets the preset standard;

[0101] If the variance of the diameter fluctuation is greater than or equal to the preset variance of the diameter fluctuation, it is determined that the preparation of the composite tubular film does not meet the preset standard, and the preset pulling speed is reduced according to the ratio of the variance of the diameter fluctuation to the preset fluctuation variance.

[0102] Specifically, through 50 times of data verification, when the variance of the diameter fluctuation is less than 0.00038 mm 2 , the size qualification rate of the finished composite film material for building is greater than 90%, and in the embodiment, the preset variance of the diameter fluctuation is 0.0004 mm 2 , but the above value is not limited thereto, and those skilled in the art can adjust the above value according to actual needs.

[0103] Specifically, the variance of the diameter fluctuation represents the stability of the size of the composite tubular film after cooling and solidification, when the variance of the diameter fluctuation is less than the preset value, it indicates that the size consistency of the composite tubular film meets the requirements of building splicing and long-term stress, and is directly determined to be qualified to ensure production efficiency; when the variance of the diameter fluctuation is greater than or equal to the preset value, it indicates that problems such as uneven cooling, insufficient coordination between pulling and cooling have been converted into actual size defects, which will lead to subsequent splicing gaps, stress cracking and other risks, and therefore is determined to be unqualified. At the same time, the pulling speed is adjusted to affect the cooling and sizing time of the film material, so as to avoid process fluctuations caused by blind adjustment.

[0104] Specifically, the reduction range of the preset pulling speed is positively correlated with the ratio of the variance of the diameter fluctuation to the preset fluctuation variance, wherein the positive correlation is, for example, linear positive correlation or nonlinear positive correlation, and the linear slope of the linear positive correlation is not specifically limited, for example, the reduction range of the preset pulling speed is set to , the ratio of the variance of the diameter fluctuation to the preset fluctuation variance is set to , then , and a is a speed adjustment coefficient, and a is set to 0.96. It can be understood that the greater the ratio of the variance of the diameter fluctuation to the preset fluctuation variance, the greater the reduction range of the preset pulling speed.

[0105] Specifically, the process of obtaining the variance of the diameter fluctuation of the composite tubular film comprises:

[0106] After the composite tubular film is cooled and solidified, a diameter of the composite tubular film is collected by using a diameter gauge at a preset collection frequency of 10 Hz within a second preset time length of 60 s;

[0107] The variance of all diameters is calculated, i.e., the diameter fluctuation variance of the composite tubular film.

[0108] Specifically, the adjustment strategy when the preparation of the composite tubular film does not meet the preset standard according to the wind speed extreme value ratio of the cooling air ring includes:

[0109] If the wind speed extreme value ratio is less than a preset wind speed extreme value ratio of 1.15, the preset processing temperature of the co-extrusion die is reduced according to the difference between the preset wind speed extreme value ratio and the wind speed extreme value ratio;

[0110] If the wind speed extreme value ratio is greater than or equal to the preset wind speed extreme value ratio, the air volume of the air outlet corresponding to the maximum wind speed of the cooling air ring is reduced according to the difference between the wind speed extreme value ratio and the preset wind speed extreme value ratio;

[0111] The wind speed extreme value ratio of the cooling air ring is the ratio of the maximum wind speed to the minimum wind speed in each air outlet of the cooling air ring, wherein a micro wind speed sensor is installed at each independent air outlet of the cooling air ring to form a circumferentially uniform wind speed monitoring array.

[0112] Specifically, the reduction range of the preset processing temperature of the co-extrusion die is positively correlated with the difference between the preset wind speed extreme value ratio and the wind speed extreme value ratio, wherein the positive correlation is, for example, linear positive correlation or nonlinear positive correlation, and the linear slope of the linear positive correlation is not particularly limited, for example, the reduction range of the preset processing temperature of the co-extrusion die is set to the difference between the preset wind speed extreme value ratio and the wind speed extreme value ratio is set to k is a temperature adjustment coefficient, and k is set to 0.94. It can be understood that the greater the difference between the preset wind speed extreme value ratio and the wind speed extreme value ratio, the greater the reduction range of the preset processing temperature of the co-extrusion die.

[0113] Specifically, the reduction range of the air volume of the air outlet corresponding to the maximum wind speed of the cooling air ring is positively correlated with the difference between the wind speed extreme value ratio and the preset wind speed extreme value ratio, wherein the positive correlation is, for example, linear positive correlation or nonlinear positive correlation, and the linear slope of the linear positive correlation is not particularly limited, for example, the reduction range of the air volume of the air outlet corresponding to the maximum wind speed of the cooling air ring is set to the difference between the wind speed extreme value ratio and the preset wind speed extreme value ratio is set to is an air volume adjustment coefficient, and ​​​It can be understood that the greater the difference between the wind speed extreme value ratio and the preset wind speed extreme value ratio, the greater the reduction range of the air volume of the air outlet corresponding to the maximum wind speed of the cooling air ring.

[0114] In this embodiment, the preset wind speed extreme value ratio is 1.15, but the above value is not limited thereto, and those skilled in the art can adjust the above value according to actual needs.

[0115] Specifically, when the wind speed extreme value ratio is less than the preset value, it indicates that the wind speed difference of each air outlet is small and the circumferential air distribution is uniform, but at this time the circumferential cooling uniformity representation value is still not up to standard, and the root cause is not the wind speed distribution problem, but the preset processing temperature of the co-extrusion die is too high, which leads to the initial temperature of the bubble being too high. Even if the wind speed is uniform, the temperature difference between the bubble surface and the cooling air is still too large, which will still cause the imbalance of the local heat dissipation rate, so reducing the preset processing temperature of the co-extrusion die can reduce the initial temperature of the bubble and reduce the temperature difference fluctuation in the cooling process, thereby optimizing the cooling uniformity from the heat conduction source. When the wind speed extreme value ratio is greater than or equal to the preset value, it indicates that the circumferential wind speed difference has exceeded the reasonable range, and the cooling of the area corresponding to the air outlet with the maximum wind speed is too fast, and the cooling of the area with the minimum wind speed is too slow, which is the direct root cause of uneven cooling. At this time, by reducing the air volume of the air outlet corresponding to the maximum wind speed, the circumferential wind speed difference is reduced and the cooling rate of each area is balanced, thereby improving the co-extrusion molding efficiency.

[0116] So far, the technical solutions of the present application have been described in combination with the preferred embodiments shown in the drawings, but those skilled in the art can easily understand that the protection scope of the present application is obviously not limited to these specific embodiments. Those skilled in the art can make equivalent changes or replacements to the related technical features without departing from the principles of the present application, and the technical solutions after the changes or replacements will fall within the protection scope of the present application.

Claims

1. A multilayer co-extrusion molding method for a composite membrane material for building applications, characterized in that, include: The polymer mixture of each layer is placed in an independent extruder and melted and plasticized at a preset maximum melting temperature difference. Then it is introduced into the co-extrusion die of a co-extrusion blown film machine and co-extruded synchronously at a preset processing temperature to obtain a composite tubular melt preform. Gas is injected into the interior of the composite tubular melt billet at a preset blowing pressure, and the composite tubular melt billet is pulled at a preset traction rate to obtain a composite tubular film bubble. Based on the outline pixel area of ​​the image of the composite tubular membrane bubble, the membrane bubble morphology stability characterization value is obtained, and the preparation of the composite tubular membrane bubble is determined according to the membrane bubble morphology characterization value to determine whether it meets the preset standard. The composite tubular membrane bubble that meets the preset standard is cooled and solidified through a cooling air ring to obtain a composite tubular membrane; Based on the circumferential temperature of the composite tubular membrane before and after cooling and solidification, the circumferential cooling uniformity characterization value is obtained. When it is determined that the preparation of the composite tubular membrane is at risk of not meeting the preset standard based on the circumferential cooling uniformity characterization value, the preparation of the composite tubular membrane is further determined based on the diameter fluctuation variance of the composite tubular membrane to determine whether the preparation of the composite tubular membrane meets the preset standard. When the preparation of the composite tubular membrane does not meet the preset standard based on the circumferential cooling uniformity characterization value, the adjustment strategy for the preparation of the composite tubular membrane does not meet the preset standard is determined based on the circumferential wind speed extreme ratio of the cooling wind ring. The adjustment strategy is to reduce the preset processing temperature or reduce the air volume of the outlet corresponding to the maximum wind speed of the cooling wind ring. The composite tubular membrane that meets the preset standards is flattened and rolled up to obtain a composite membrane material for building.

2. The multilayer co-extrusion molding method for architectural composite membrane materials according to claim 1, characterized in that, The polymer mixtures of each layer are respectively a mixture of linear low-density polyethylene, antioxidant and ultraviolet absorber for the outer layer; a mixture of linear low-density polyethylene, polyolefin elastomer, ethylene-butyl acrylate copolymer and reinforcing filler for the middle layer; and a mixture of linear low-density polyethylene and ethylene-butyl acrylate copolymer for the inner layer.

3. The multilayer co-extrusion molding method for architectural composite membrane materials according to claim 1, characterized in that, The process of determining whether the preparation of the composite tubular membrane vesicle meets the preset standard based on the membrane vesicle morphology characterization values ​​includes: The membrane vesicle morphology characterization values ​​are compared with the first preset membrane vesicle morphology characterization values ​​and the second preset membrane vesicle morphology characterization values, respectively. If the membrane morphology characterization value is less than the first preset membrane morphology characterization value, then the preparation of the composite tubular membrane vesicle is determined to meet the preset standard. If the membrane bubble morphology characterization value is greater than or equal to the first preset membrane bubble morphology characterization value and less than the second preset membrane bubble morphology characterization value, then it is determined that the preparation of the composite tubular membrane bubble does not meet the preset standard, and the preset inflation pressure is increased according to the difference between the membrane bubble morphology characterization value and the first preset membrane bubble morphology characterization value. If the membrane bubble morphology characterization value is greater than or equal to the second preset membrane bubble morphology characterization value, it is determined that the preparation of the composite tubular membrane bubble does not meet the preset standard, and the preset maximum melting temperature difference is reduced according to the difference between the membrane bubble morphology characterization value and the second preset membrane bubble morphology characterization value.

4. The multilayer co-extrusion molding method for architectural composite membrane materials according to claim 3, characterized in that, The process of obtaining the characterization values ​​for membrane vesicle morphology stability includes: Within a first preset time period, a number of orthographic images of the composite tubular membrane bubble are captured at a preset frequency. Extract the pixel area enclosed by the outline of the composite tubular membrane bubble in each image; Calculate the standard deviation of the area of ​​all pixels and denote it as the morphological stability characterization value of the bubble.

5. The multilayer co-extrusion molding method for architectural composite membrane materials according to claim 4, characterized in that, Several temperature difference adjustment methods are provided to reduce the preset maximum melting temperature difference, and each temperature difference adjustment method reduces the preset maximum melting temperature difference by a different amount.

6. The multilayer co-extrusion molding method for architectural composite membrane materials according to claim 5, characterized in that, The process of determining whether the preparation of the composite tubular membrane meets the preset standard based on the circumferential cooling uniformity characterization value of the composite tubular membrane includes: The circumferential cooling uniformity characterization value is compared with the first preset circumferential cooling uniformity characterization value and the second preset circumferential cooling uniformity characterization value, respectively. If the circumferential cooling uniformity characterization value is less than the first preset circumferential cooling uniformity characterization value, then the preparation of the composite tubular membrane is determined to meet the preset standard. If the circumferential cooling uniformity characterization value is greater than or equal to the first preset circumferential cooling uniformity characterization value and less than the second preset circumferential cooling uniformity characterization value, it is determined that the preparation of the composite tubular membrane has a risk of not meeting the preset standard, and the preparation of the composite tubular membrane is determined a second time based on the diameter fluctuation variance of the composite tubular membrane to determine whether the preparation of the composite tubular membrane meets the preset standard. If the circumferential cooling uniformity characterization value is greater than or equal to the second preset circumferential cooling uniformity characterization value, it is determined that the preparation of the composite tubular membrane does not meet the preset standard, and the adjustment strategy when the preparation of the composite tubular membrane does not meet the preset standard is determined according to the extreme ratio of the circumferential wind speed of the cooling wind ring.

7. The multilayer co-extrusion molding method for architectural composite membrane materials according to claim 6, characterized in that, The process of obtaining the circumferential cooling uniformity characterization value includes: Before cooling and solidification, the temperature of several circumferentially set monitoring points of the composite tubular membrane to be cooled is collected; After cooling and solidification, the temperature at the monitoring points is collected; Calculate the difference between the temperature before cooling and the temperature after cooling at each monitoring point, and record it as the cooling temperature difference at each monitoring point; The standard deviation of all cooling temperature differences is denoted as the circumferential cooling uniformity characterization value.

8. The multilayer co-extrusion molding method for architectural composite membrane materials according to claim 7, characterized in that, If the preparation of the composite tubular membrane does not meet the preset standard, the preset traction rate is reduced based on the ratio of the diameter fluctuation variance to the preset fluctuation variance, according to the comparison result of the diameter fluctuation variance being greater than or equal to the preset diameter fluctuation variance.

9. The multilayer co-extrusion molding method for architectural composite membrane materials according to claim 8, characterized in that, The process of obtaining the diameter fluctuation variance of the composite tubular membrane includes: After the composite tubular membrane is cooled and solidified, the diameters of several composite tubular membranes are collected at a preset sampling frequency within a second preset time period. The variance of all diameters is calculated, which is the diameter fluctuation variance of the composite tubular membrane.

10. The multilayer co-extrusion molding method for architectural composite membrane materials according to claim 9, characterized in that, Adjustment strategies for when the preparation of the composite tubular membrane does not meet the preset standards, based on the extreme ratio of the cooling air ring's wind speed, include: If the extreme wind speed ratio is less than the preset extreme wind speed ratio, the preset processing temperature of the co-extrusion die is reduced according to the difference between the preset extreme wind speed ratio and the extreme wind speed ratio. If the extreme wind speed ratio is greater than or equal to the preset extreme wind speed ratio, the air volume of the outlet corresponding to the maximum wind speed of the cooling air ring is reduced according to the difference between the extreme wind speed ratio and the preset extreme wind speed ratio. The extreme wind speed ratio of the cooling air ring is the ratio of the maximum wind speed to the minimum wind speed at each air outlet of the cooling air ring.

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