CN115926296B

CN115926296B - Polymer foaming sheet and manufacturing method and application thereof

Info

Publication number: CN115926296B
Application number: CN202310010801.5A
Authority: CN
Inventors: 张鑫; 魏琼
Original assignee: Hubei Xiangyuan New Material Technology Inc
Current assignee: Hubei Xiangyuan New Material Technology Inc
Priority date: 2023-01-05
Filing date: 2023-01-05
Publication date: 2024-06-04
Anticipated expiration: 2043-01-05
Also published as: CN115926296A

Abstract

The invention discloses a polymer foaming sheet and a manufacturing method and application thereof. The polymer foaming sheet has the integral structure of a gas/solid two-phase composite material which takes an irradiation crosslinked polymer as a continuous phase and takes bubbles formed by gas molecules as a disperse phase, wherein the VA content of the continuous phase is less than 8%, the volume fraction of nitrogen in the gas molecules of the disperse phase is more than 60%, the volume fraction of ammonia is less than 3%, and the surface structure of the polymer foaming sheet meets the following conditions: the surface property transverse-longitudinal ratio Str is more than 0.6; the maximum valley depth Sv is less than 20 μm; the polymer foaming sheet provided by the invention is applied to portable electronic products and intelligent wearable equipment, plays roles in sealing, dust prevention and water prevention, can meet the narrow frame requirements of miniaturized electronic equipment through the examination of extreme use environments such as high and low temperature, dust, water vapor and the like, and can not reduce the sealing, dust prevention and water prevention performance in the use process.

Description

Polymer foaming sheet and manufacturing method and application thereof

Technical Field

The invention relates to the field of polymer composite materials, in particular to a polymer foaming sheet which is applied to portable electronic products and intelligent wearable equipment and has the functions of sealing, dust prevention and water prevention.

Background

With the development of 5G technology, the portable electronic product has diversified application scenes, and the three-proofing performance, namely, dustproof, waterproof and shockproof performance plays a key role in normal use of the electronic product under severe environmental conditions and in special application occasions.

In the past, electronic products can use materials such as PET to seal between a screen and a shell, but when a PET adhesive tape with higher hardness is used as a sealing material between a touch control layer and a liquid crystal display layer of a product screen, the shock absorption and buffering performance of the electronic products can be reduced, and the risk of damaging the electronic products when the electronic products fall or collide carelessly can be increased.

The polymer foaming material is an environment-friendly polymer foaming material, is generally used as a waterproof material for a frame, a screen bottom buffer, a rear cover middle frame and a dustproof material for an intelligent watch of a smart phone in the field of portable electronic products, and has a wide market prospect. As intelligent wearable devices are transformed into health life auxiliary functions, wearable intelligent devices carrying more health monitoring or auxiliary functions such as heart rate measurement, drop alarm and sports reminding functions will be increasingly valued. But the unavoidable environment that needs contact water stain, dust etc. in the use scene, consequently develop one kind portable electronic product and intelligent wearable in the equipment play sealed, dustproof and waterproof effect polymer foaming thin slice to guarantee its good dustproof waterproof performance under the narrower condition of cross cutting width.

When the dustproof and waterproof foaming material product in the prior art is used by die-cutting into a narrow frame with the width smaller than 1mm, the deformation recovery capability of the foaming sheet is reduced due to the fact that the proportion of damaged bubbles in unit volume is increased due to the fact that the die-cutting width is narrow, the dustproof and waterproof performance is poor, and the inside of the electronic product is more easily invaded by dust and water vapor when the electronic product is used under extreme conditions.

Disclosure of Invention

Aiming at the defects of the prior art, the invention aims to provide a polymer foaming sheet and a manufacturing method thereof, and aims to solve the problem that the dustproof and waterproof performance is poor when the traditional dustproof and waterproof foaming material product is applied in a mode of being die-cut into a narrower size.

The invention is realized in the following way:

The invention provides a polymer foaming sheet, which has an integral structure of a gas/solid two-phase composite material which takes an irradiation crosslinked polymer as a continuous phase and gas bubbles formed by gas molecules as a disperse phase, wherein the VA content of the continuous phase is less than 8%, the gas molecules of the disperse phase contain nitrogen, carbon monoxide and ammonia, the volume fraction of the nitrogen is more than 60%, and the volume fraction of the ammonia is less than 3%.

Further, the polymer foam sheet has an upper and lower surface structure perpendicular to the thickness direction satisfying the following conditions: the surface property transverse-longitudinal ratio Str is more than 0.6; the maximum valley depth Sv is smaller than 20 mu m, and the Str and Sv are three-dimensional surface property parameters in ISO 25178.

Further, the thickness of the polymer foam sheet is 0.05-0.5mm, and the average diameter of the bubbles in the polymer foam sheetLess than 300 μm.

Further, the thickness change rate X1 of the polymer foam sheet after being subjected to high-temperature treatment at 70 ℃ is as follows: x1 is more than or equal to 10 percent and less than or equal to 10 percent; the thickness change rate X2 after the low-temperature treatment at the temperature of minus 20 ℃ is as follows: x2 is more than or equal to 10 percent and less than or equal to 10 percent.

Further, the average thickness loss rate of the polymer foam sheet after being die-cut into 25mm x 25mm narrow frame materials with the width of 1mm is less than 5%.

The invention also provides a method for manufacturing the polymer foaming sheet, which comprises the following steps:

Resin sheet molding step: uniformly mixing and extruding the polymer foaming sheet raw materials through a double-screw extruder to prepare a resin sheet with uniform thickness;

A resin sheet irradiation modification process: performing irradiation modification on the prepared resin sheet by using an electron beam;

High-temperature foaming process of resin sheet: and decomposing the foaming agent by the resin sheet after irradiation modification in a high-temperature environment to obtain the polymer foaming sheet.

Specifically, in the resin sheet molding process, the polymer rheological parameter monitored on line in the production process of the twin-screw extruder should meet the shearing speed of 200S ^-1 to 500S ^-1 and the melt viscosity of 400 pa.s to 800 pa.s.

Specifically, in the resin sheet irradiation modification procedure, the prepared resin sheet is subjected to irradiation modification by using an electron beam, the irradiation dose is 100 kilogray (KGy) to 300 kilogray (KGy), and the fluctuation range of the real-time linear speed of the resin sheet transmission in the irradiation process is up to and down to 3% of the preset speed.

Specifically, in the high-temperature foaming process of the resin sheet, a heating mode of combining steam heating and hot air heating is adopted, the length of a heat preservation section after foaming is 5-10m, and the temperature of the heat preservation section is 60-80 ℃.

The polymer foaming sheet disclosed by the invention is applied to sealing, dust prevention and water prevention of portable electronic products and intelligent wearable equipment.

The invention has the following beneficial effects:

The polymer foaming sheet disclosed by the invention has the advantages that the structural parameters and the performance test structure can meet the use requirement of die-cutting into narrow frames in small electronic equipment, and the sealing, dust-proof and water-proof performances are not reduced in the use process.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below. The specific conditions are not noted in the examples and are carried out according to conventional conditions or conditions recommended by the manufacturer. The reagents or apparatus used were conventional products commercially available without the manufacturer's attention.

Integral structure

The invention provides a polymer foaming sheet, the integral structure of which is a gas/solid two-phase composite material taking irradiation crosslinked polymer as a continuous phase and gas bubbles formed by gas molecules as a disperse phase, the polymer foaming sheet formed by the gas bubbles and resin can provide good sealing dustproof and waterproof performances, the gas molecules serving as the disperse phase are bound in the polymer, and the polymer foaming sheet can be compressed in the thickness direction in the use process, so that the gas holes are deformed to cause the compression of the gas molecules, and a reaction force is provided for the surface to be sealed so as to prevent the entry of external dust and water vapor.

Furthermore, the VA content of the continuous phase of the polymer foaming sheet is less than 8%, the continuous phase is modified by using EVA resin in the polymer foaming sheet, and the addition of the EVA resin reduces the processing difficulty of the polymer foaming sheet in the resin sheet forming process, so that the polymer foaming sheet is softer and is beneficial to improving the buffering performance of the foaming sheet. However, in order to ensure the dustproof and waterproof performance of the polymer foaming sheet, the VA content of the continuous phase needs to be less than 8%, the compliance of a continuous phase molecular chain can be changed due to the fact that the VA content is too large, the molecular chain movement capability is increased, creep is easier to occur during compression use, the compression stress is reduced under the condition of the same compression ratio, the dustproof and waterproof performance of the polymer foaming sheet is reduced, on the other hand, the shearing viscosity of a system can be reduced due to the fact that high-melting-point materials in a formula are harder to mix uniformly due to the fact that the VA content is too large, and two negative effects are caused by the fact that the materials which are not mixed uniformly: 1. the surface structure of the polymer foaming sheet is seriously influenced, projections are formed on the surface of the resin which is not uniformly mixed, the contact area between the surface of the polymer foaming sheet and the surface of sealing equipment is reduced, and the dustproof and waterproof performance is reduced; 2. the dimensional stability in the use process is affected, the resin which is not uniformly mixed plays the same role as impurities in the foaming process, so that the aperture ratio of the polymer foaming sheet is increased, the dimensional stability of the polymer foaming sheet in the use under a high/low temperature environment is affected, and the thickness loss rate when the polymer foaming sheet is die-cut into a narrow frame is also larger.

Further, the volume fraction of nitrogen in the disperse phase is more than 60%, and the volume fraction of ammonia is less than 3%. The polymer foaming sheet uses azo foaming agent, wherein the thermal decomposition process of Azodicarbonamide (AC) is divided into three stages, wherein the gas phase product of the first stage is nitrogen, carbon monoxide, isocyanic acid (HNCO), and the solid residue is biurea; the gas phase products of the second stage are ammonia gas and HNCO; the gas phase products of the third stage are ammonia gas, carbon dioxide, and the solid residues are urea, etc. The gas molecules in the dispersed phase are mainly: the diffusion speed of nitrogen in the polymer material is slower, and when the gas molecules in the disperse phase are mainly nitrogen, the thickness change rate of the polymer foam sheet in the high/low temperature environment test process is smaller due to the low transmittance of the nitrogen molecules, so that the polymer foam sheet has good dustproof and waterproof properties. The volume fraction of nitrogen in the polymer foaming sheet is more than 60%, and the volume fraction of ammonia is less than 3%, which indicates that the main reaction of the foaming agent AC decomposition is activated, thereby being beneficial to meeting the environmental protection requirement that the azo residue rate of the polymer foaming sheet in electronic products is less than 0.1%, on the other hand, the second-stage reaction and the third-stage reaction are lagged, and the adverse effects of equipment corrosion and the like caused by decomposing out the gas with pungent smell of ammonia and HNCO are avoided.

Surface structure

The surface structure of the polymer foaming sheet provided by the invention is as follows: the surface property transverse-longitudinal ratio Str is more than 0.6; the maximum valley depth Sv is less than 20 μm. Str and Sv are three-dimensional surface property parameters in ISO25178, str is a surface shape aspect ratio, and indicates anisotropy and isotropy of a surface shape. The values are 0-1,0 indicates that stripes exist, 1 indicates that the direction is not dependent, the value of Str is closer to 0 to indicate that the surface texture of the polymer foam sheet has orientation, and the test shows that the polymer foam sheet with the same surface roughness has higher surface texture orientation degree, namely the value of Str is closer to 0, the waterproof performance of the polymer foam sheet is poorer, and the liquid inlet path is always along the orientation direction of the surface texture. Sv is the maximum valley depth, representing the maximum value of the surface pit area depth. The sealing performance of the polymer foaming sheet is affected by the fact that the maximum valley depth is too large, so that the dustproof and waterproof performance is poor, defects are formed on the surface structure of the polymer foaming sheet due to the fact that the depth of the concave area is large, the polymer foaming sheet is easier to break when pulled up, and the elongation rate of the material is reduced. Thus, in order to achieve the above object, the present invention provides a polymer foam sheet having a surface structure satisfying: the surface property transverse-longitudinal ratio Str is more than 0.6; the maximum valley depth Sv is less than 20 μm.

The type of resin constituting the polymer foam sheet is a foam base material conventional in the art and is selected from ethylene-vinyl acetate copolymer, polyethylene resin, polypropylene resin, and the like. The ethylene-vinyl acetate copolymer preferably has a vinyl acetate content of 8% to 20%.

The polyethylene-based resin is not particularly limited, and includes, but is not limited to, low-density polyethylene, medium-density polyethylene, high-density polyethylene, linear low-density polyethylene, and the like, and alternatively, an ethylene- α -olefin copolymer mainly composed of ethylene may be selected, wherein the α -olefin is selected from α -olefins having 2 to 12 carbon atoms each, such as propylene (propylene), 1-butene, 1-pentene, 3-methyl-1-butene, 1-hexene, 3-methyl-1-pentene, 4-methyl-1-pentene, 3-ethyl-1-pentene, 1-octene, 1-decene, and 1-undecene. The number of kinds of such alpha-olefins may be only 1, or may be 2 or more. The above polyethylene-based resins may be used singly or in combination of two or more, and among them, linear low-density polyethylene resins are preferable.

The azo compound is foamed uniformly and controllably, and specifically comprises the following steps: azodicarbonamide, diisopropyl azodicarbonate, metal azodicarbonate (such as barium azodicarbonate), azobisisobutyronitrile, and the like, and azodicarbonamide is more preferable.

The use of the foaming auxiliary agent is favorable for adjusting the decomposition temperature and decomposition speed of the foaming agent, and the foaming auxiliary agent matched with the azo foaming agent comprises urea foaming auxiliary agents, phosphate foaming auxiliary agents, organic acid foaming auxiliary agents, metal salt foaming auxiliary agents and the like, and glycerin, zinc stearate, zinc oxide and zinc acetate are further preferred.

Other functional additives can be added according to actual requirements to further improve various properties of the polymer foam sheet, and the properties can be listed as follows: antioxidants, light stabilizer antimicrobials, colorants, antistatic agents, and fillers. Wherein the antioxidant is preferably one or more of BASF IRGAFOS 168 antioxidant and BASF Irganox1010 antioxidant; the light stabilizer is preferably one or more of BASF TINUVIN 783FDL high molecular weight light stabilizer and BASF Chimassorb 944 light stabilizer.

Method of manufacture

The invention provides a polymer foaming sheet, which comprises the following steps:

Resin sheet molding step: uniformly mixing and extruding the polymer foaming sheet raw material through a double-screw extruder to prepare a resin sheet with uniform thickness;

Further, the polymer foam sheet raw material includes a resin constituting a continuous phase of the foam sheet, a foaming agent capable of generating a gas of a dispersed phase of the foam sheet, and an activator of the foaming agent.

Furthermore, the resin sheet molding process adopts a double-screw extruder to extrude the polymer foaming sheet raw material into the resin sheet with uniform thickness, and the double-screw extruder has strong mixing capability and is more suitable for polymer blending modification. Meanwhile, compared with a single screw extruder, the expansion ratio of the resin sheet extruded by the double screws in the transverse direction can be larger, the expansion in the transverse direction can weaken the molecular chain orientation of the polymer foaming sheet caused by longitudinal stretching in the foaming process, the requirement that the surface property transverse-longitudinal ratio str of the polymer foaming sheet is larger than 0.6 can be met, and the orientation degree of the polymer foaming sheet in the longitudinal direction can be reduced.

Further, the twin screw extruder is equipped with an in-line viscosity testing device between the extruder and the die, and continuously monitors the in-line rheological parameters of the polymer. The rheological property of the polymer material can directly reflect the extrusion processing property of the material and is used for controlling key technological parameters of the polymer foaming sheet in the double-screw extrusion process to meet the following conditions: the temperature of the melt is 100-130 ℃, the shear rate is 200S ^-1-500S^-1, and the melt viscosity is 400 pa.s-800 pa.s. For extrusion processing of a blending system, the rheological property of materials is related to the mixing degree (uniformity degree) of the system, parameters such as melt shear rate, viscosity and the like in the operation process of a double-screw extruder are monitored through an online viscosity testing device, the stability of resin melt flow in the production process can be increased by controlling the range, the uniformity degree of material mixing is improved, the surface evenness of a resin sheet manufactured by the process is good, the thickness is uniform, and the surface evenness of a polymer foaming sheet in the foaming process is improved to ensure that the maximum valley depth Sv of the polymer foaming sheet is smaller than 20 mu m.

Further, in the sheet irradiation modification procedure, the electron beam is used for carrying out irradiation modification on the prepared resin sheet, the irradiation dose is 100 kilogray (KGy) to 300 kilogray (KGy), and the polymer foaming sheet with the irradiation dose range has more uniform and finer foam cells, so that the average diameter of the foam bubbles of the polymer foaming sheet can be achievedRequirements of less than 300 μm.

The resin sheet is transported by a transportation belt process under a scanning beam, the real-time linear speed of the resin sheet transportation in the irradiation process only allows fluctuation within a range of 3% above and below a preset speed, the longitudinal dose absorption uniformity of the resin sheet is mainly influenced by the sheet transportation speed, the non-uniformity of the polyolefin sheet absorption dose can be represented by the difference of crosslinking degree, the thickness and the density of the product can be different in foaming, the breadth can also fluctuate, and the requirement of the real-time linear speed of the resin sheet irradiation is strictly controlled within the range in order to ensure the stability of the polymer foaming sheet in the production and use processes.

Further, in the high-temperature foaming step of the resin sheet, the resin sheet is heated by a combination of steam heating and hot air heating to decompose the foaming agent, so as to obtain the polymer foam sheet. The steam heating has the advantages of high heat efficiency, low energy consumption and high heating speed, but the heating temperature is lower, the foaming agent is possibly decomposed insufficiently by singly using the steam heating mode for foaming, and the problems of lower multiplying power and high azo residual rate of the polymer foaming sheet can occur; the hot air heating mode has low heat efficiency, high energy consumption and poor temperature uniformity, and can keep a local area at a higher temperature level so as to quickly decompose the foaming agent; the invention adopts a mode of combining steam heating and hot air heating to heat the resin sheet, the whole area adopts a mode of heating by a steam radiator to keep the temperature in the foaming bin at 150-180 ℃, and the foaming section adopts a mode of hot air heating to raise the temperature of the foaming area to 300-350 ℃. The heating mode can be used for reducing energy consumption, keeping temperature uniformity in the foaming process, reducing the influence of poor uniformity of hot air heating temperature on the structure and appearance of the foaming sheet, and improving the uniformity of air holes and surface structures of the polymer foaming sheet so as to meet the requirements of dust prevention and water prevention when the polymer foaming sheet is applied to a narrower size through die cutting.

Further, the high-temperature foaming process of the resin sheet needs to be subjected to a heat preservation section with the length of 5-10 m after foaming, the temperature of the heat preservation section is 60-80 ℃, after the polymer foaming sheet is foamed from the high-temperature foaming area, if the polymer foaming sheet directly enters into the room-temperature environment, quenching of the surface structure is caused, and the surface structure and the inside of the foaming sheet have temperature difference, so that oriented shrinkage occurs on the surface of the polymer foaming sheet, and the orientation degree of the surface texture is increased. The heat preservation section with the length of 5-10 meters is arranged after the high-temperature foaming process of the resin sheet, the temperature of the heat preservation section is 60-80 ℃, the cooling process of the polymer foaming sheet can be slowed down, and the influence on the dust-proof and waterproof performance of the polymer foaming sheet due to the fact that the three-dimensional surface property parameter Str (surface shape transverse-longitudinal ratio) is smaller than 0.6 is prevented.

Measurement method

Determination of continuous phase VA content of polymer foam sheet

The saponification method is adopted to measure the content of the continuous phase VA, and the measurement method is as follows: accurately weighing 1g (accurate to 0.0001) of the polymer foam sheet, adding into a conical flask, weighing 20ml of toluene and 5 mlKOH-ethanol solution, adding into the conical flask, installing a reflux condenser, and heating at 90 ℃ for reaction for about 4 hours. After the saponification reaction is completed, the reaction solution is cooled to room temperature, 30ml of ethanol with the concentration of 95 percent, 15ml of distilled water and 4-5 drops of thymol blue indicator are added, 0.1NH ₂SO₄ is used for titration until the liquid turns yellow from blue, and the consumption Vml of H ₂SO₄ is recorded. This procedure was repeated, a blank experiment was performed (EVA was not added and heating was not performed) and the amount of H ₂SO₄ used was recorded as V0ml. The percentage of VA was calculated from the formula:

VA％＝MN(V0-V)/1000G×100％；

Wherein G is the mass (G) of the polymer foam sheet sample;

N: equivalent concentration of sulfuric acid for titration;

m: molecular weight of vinyl acetate (86.09);

V0 and V titration of the volume (ml) of sulfuric acid consumed by the blank and saponification liquor.

Determination of gas content of dispersed phase of polymer foam sheet

And placing 100-200g of polymer foaming sheet in a 500ml gas collecting bottle, heating to above the melting point of the polymer foaming sheet under the protection of argon gas to enable gas molecules in bubbles to escape, cooling to room temperature, testing the gas molecules by using a trace gas analyzer, analyzing to obtain the components and the content of the gas molecules in the cells, and calculating the volume fractions of nitrogen and ammonia.

The trace body analyzer adopts a high-frequency high-voltage power supply to ionize gas, positive charge ions and free electrons are generated, a plasma environment is formed, and gas molecules to be detected are ionized into atoms. The positive charge ions and free points are accelerated to move to the negative electrode and the positive electrode respectively under the action of an electric field. As a result of collisions, ions and electrons transfer their own energy to atoms, so that the gaseous atoms are excited. After the atoms are excited, the outer electrons of the atoms undergo energy level transition, and characteristic spectra are emitted when the atoms return to the ground state. By detecting the characteristic spectrum, the concentration of trace gas is analyzed. The sample gas conditions of the trace gas analyzer are as follows: 5-40 ℃, sample gas flow rate: 50mL/min, dust content: and less than or equal to 0.1um.

Measurement of three-dimensional surface Property parameters Str, sv

In the case where the three dimensional surface property parameters (surface roughness parameters) in the international standard (ISO 25178) are Str and Sv are different from the two dimensional line roughness parameters obtained by the contact roughness meter, and the difference in the parameters such as the arithmetic average roughness Sa and the maximum height Sz which are commonly used in the two dimensional parameters is not large, three dimensional parameter values of Ssk (skewness: the degree of skewness of the height distribution with respect to the average surface), sal (shortest autocorrelation length) and Str (surface property aspect ratio: anisotropy of the surface texture) which are related to the height direction are greatly different.

According to the invention, the three-dimensional surface roughness parameter of the polymer foaming sheet can be measured by adopting a 3D measuring laser microscope. The surface texture anisotropism which cannot be represented by the two-dimensional parameters can be evaluated in a numerical mode through the three-dimensional surface roughness parameters.

Average diameter of continuous phase cells

And processing a cross-section scanning electron microscope image of the polymer foaming sheet material brittle failure by using particle size analysis statistical software to obtain the average diameter of cells. The average diameter of the bubbles was calculated as: in the/> For the average cell diameter, n is the number of cells in the scanning electron micrograph, di is the diameter of the ith cell in the scanning electron micrograph.

Loss rate of die-cut thickness

The initial thickness of the polymer foaming sheet is tested after the polymer foaming sheet is placed for 24 hours in a standard environment (the temperature is 23+/-2 ℃ and the relative humidity is 45% -55%), the polymer foaming sheet is die-cut into 25mm x 25mm, the quadrangular narrow frame material with the width of 1mm is placed for 24 hours in the standard environment (the temperature is 23+/-2 ℃ and the relative humidity is 45% -55%), the die-cut thickness of the polymer foaming sheet is tested, and the thickness loss rate of the polymer foaming sheet after die cutting is calculated.

Thickness change rate after high/low temperature treatment

The initial thickness of the polymer foam sheet is tested after the polymer foam sheet is placed for 24 hours in a standard environment (the temperature is 23+/-2 ℃ and the relative humidity is 45% -55%), the polymer foam sheet is placed in a high/low temperature test box (the high temperature is 70 ℃ and the low temperature is-20 ℃) for 6 hours, the thickness of the polymer foam sheet is tested after the polymer foam sheet is placed for 24 hours in the standard environment (the temperature is 23+/-2 ℃ and the relative humidity is 45% -55%), the thickness after the high/low temperature treatment is tested, and the thickness change rate after the high/low temperature treatment is calculated.

Dust proof test

According to the sand test: the test was performed according to GB/T2423.37-2006 standard.

Waterproof test

The polymer foam sheet was die cut into narrow frame samples (25 mm x 25mm, frame width 1 mm), placed between two acrylic plates, the compression ratio of the samples was defined to be 50% using a limiting gasket, and the acrylic plates were secured by screw tightening (acrylic plate thickness 20.+ -. 1mm; flatness < 0.015mm; surface roughness Ra < 0.1 μm). The whole acrylic plate is put into water, the water depth is 30cm, the time of water drops in the inner frame of the sample after the acrylic plate is put into water is recorded, the waterproof performance is judged according to the time, the water inlet time is more than 20min, and the water inlet time is judged to be qualified and is marked as OK; and judging that the water inflow is unqualified within 20min, and marking the water inflow as NG.

The present invention will be described in further detail with reference to examples and comparative examples.

Example 1

A method of manufacturing a polymer foam sheet comprising the steps of:

(1) 45 parts of polyethylene resin, 30 parts of POE resin, 25 parts of EVA resin, 2 parts of AC foaming agent, 1 part of foaming auxiliary agent, 0.5 part of antioxidant and 0.5 part of light stabilizer are uniformly mixed, and then a double-screw extruder is used for preparing a resin sheet with uniform thickness, the melt viscosity is controlled to be 670 pa-S, and the shear rate is controlled to be 250S ^-1.

(2) The prepared resin sheet is subjected to irradiation modification by using an electron beam, the irradiation dose is 190 kilogray (KGy), the resin sheet is transported by a conveyor belt process under a scanning beam, the transmission line speed is set to be 30m/min, and the real-time line speed range of the resin sheet transportation in the irradiation process is 30+/-0.5 m/min.

(3) The irradiated resin sheet is foamed at high temperature, and the resin sheet is heated by adopting a mode of combining steam heating and hot air heating to decompose a foaming agent to obtain a polymer foaming sheet, wherein the temperature of a foaming area is 320 ℃, the length of a heat preservation section after foaming is 8m, and the temperature of the heat preservation section is 60 ℃.

The polyethylene resin is a low density polyethylene resin. (petrochemical 951-050 in Low Density polyethylene resin LDPE)

The POE resin is a copolymer of ethylene and butene. (Mitsui chemical POE TAFMER ^TM DF 110)

The EVA resin is ethylene-vinyl acetate copolymer. (Taiwan table plastic EVA TAISOX 7350M)

The foaming auxiliary agent is zinc oxide.

The antioxidant is a BASF IRGAFOS 168 antioxidant and a BASF Irganox1010 antioxidant.

The light stabilizer is BASF TINUVIN 783FDL high molecular weight light stabilizer.

The polymer foam sheet prepared according to the method of example 1 has the structural parameters and the performance test results shown in the following table 1, and can meet the requirement of good dustproof and waterproof performance when being used by being cut into narrow frames.

Examples 2 to 3

Based on the above example 1, the polymer foaming sheet with the structural parameters and the performance test structure meeting the requirements of dust prevention and water resistance of the narrow frame is prepared by adjusting the formula and the processing technology, and the specific formula and the processing technology are shown in the following table examples 2-3.

Comparative examples 1 to 3

Based on the embodiment 1, the formula and the processing technology are adjusted, the specific formula and the processing technology are shown in the following table, the comparative examples 1-3, and the polymer foaming sheets prepared in the comparative examples 1-3 can not meet the requirements of dust prevention and water prevention of narrow frames.

Table 1 material formulations, manufacturing process parameters and performance test results for examples and comparative examples

The data in the table can be obtained, compared with the comparative example, the polymer foaming sheet prepared by the embodiment of the invention has small thickness change rate after die cutting and high/low temperature environment of manager, has good dustproof and waterproof performance, and can meet the use requirement of die cutting into narrow frames in small electronic equipment.

The above description is only of the preferred embodiments of the present invention and is not intended to limit the present invention, but various modifications and variations can be made to the present invention by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. The polymer foaming sheet is characterized in that the whole structure is a gas/solid two-phase composite material which takes an irradiation crosslinked polymer as a continuous phase and takes bubbles formed by gas molecules as a disperse phase, the raw materials of the polymer foaming sheet comprise foaming resin base materials, EVA resin and azo foaming agents, wherein the VA content of the continuous phase is less than 8%, the gas molecules of the disperse phase contain nitrogen, carbon monoxide and ammonia, the volume fraction of the nitrogen is more than 60%, and the volume fraction of the ammonia is less than 3%;

The upper and lower surface structures perpendicular to the thickness direction satisfy the following conditions: the surface property transverse-longitudinal ratio Str is more than 0.6; the maximum valley depth Sv is smaller than 20 mu m, and the Str and Sv are three-dimensional surface property parameters in ISO 25178;

The thickness of the polymer foam sheet is 0.05-0.5mm, and the average diameter of the bubbles in the polymer foam sheet Less than 300 μm.

2. The polymer foam sheet according to claim 1, wherein the thickness change rate X1 of the polymer foam sheet after being subjected to a high temperature treatment at 70 ℃ satisfies: x1 is more than or equal to 10 percent and less than or equal to 10 percent; the thickness change rate X2 after the low-temperature treatment at the temperature of minus 20 ℃ is as follows: x2 is more than or equal to 10 percent and less than or equal to 10 percent.

3. The polymeric foam sheet of claim 1, wherein the average thickness loss after die cutting into 25mm x 25mm, a narrow border material having a border width of 1mm is less than 5%.

4. A method for producing the polymer foam sheet according to claim 1 to 3, comprising the steps of:

Resin sheet molding step: uniformly mixing and extruding the polymer foaming sheet raw materials through a double-screw extruder to prepare a resin sheet;

High-temperature foaming process of resin sheet: and (3) decomposing the foaming agent by the irradiation modified resin sheet in a high-temperature environment to obtain the polymer foaming sheet.

5. The method according to claim 4, wherein in the resin sheet molding step, the polymer rheological parameter of the twin-screw extruder monitored on line during the production is required to satisfy a shear rate of 200S ^-1 to 500S ^-1 and a melt viscosity of 400 pa.s to 800 pa.s.

6. The method according to claim 4, wherein in the irradiation modification step of the resin sheet, the resin sheet is subjected to irradiation modification by using an electron beam at a dose of 100 KGy to 300 KGy, and a fluctuation range of a real-time linear velocity of the resin sheet transfer during irradiation is up to 3% of a predetermined velocity.

7. The method according to claim 4, wherein in the high-temperature foaming step of the resin sheet, a heating method comprising a combination of steam heating and hot air heating is used, the length of the heat-insulating section after foaming is 5 to 10m, and the temperature of the heat-insulating section is 60 to 80 ℃.

8. The use of the polymer foam sheet of claims 1-3 for sealing, dust and water proofing of portable electronic products and smart wearable devices.