Preparation method of burr-free high-elastic PVA cleaning brush

Abstract

The invention discloses a preparation method of a burr-free high-elastic PVA cleaning brush, and belongs to the technical field of polymer foaming material manufacturing. According to the method, a FEP heat shrinkage film shrinkage wrapping mold process is innovatively adopted, and the mold is subjected to heat shrinkage treatment at the temperature of 120-150 DEG C, so that gapless sealing of the surface of the mold is achieved; in the solution preparation stage, defoaming agent adding and vacuum defoaming dual treatment are synchronously carried out, so that the gas content of PVA reaction liquid is controlled to be 0.5 vol% or below; after injection molding, hole bubbles are eliminated through centrifugal treatment at the speed of 100-500 r / min, and finally gradient foaming molding is conducted at the temperature of 30-80 DEG C. Compared with a traditional sleeve mold process, the sleeve mold process has the advantages that the comprehensive reject ratio of products is reduced from 25% or above to 5% or below through a three-stage cooperative control technology (mold sealing reinforcement, solution defoaming optimization and filling power compensation), and the sleeve mold process is particularly suitable for industrial production of high-end sponge products such as medical instruments and precision wipers.

Description

Technical Field

[0001] The present invention relates to the technical field of foaming and molding of polymer materials, and particularly to a preparation method of a hairless and highly elastic PVA cleaning brush. Background Art

[0002] Polyvinyl alcohol (PVA) water-soluble cleaning brushes are widely used in high-precision cleaning fields such as medical devices and optical lenses due to their degradability and non-scratching characteristics. However, the traditional preparation process has the following key technical defects, which seriously restrict the product qualification rate and cleaning performance: Sealing failure of the sleeve mold leads to appearance defects: The traditional process uses a sleeve mold, and the initial sliding fit clearance between its end cover and the shaft core is designed to be 0.05 - 0.1 mm. However, after continuously producing 2,000 pieces, due to the difference in the thermal expansion coefficients of the mold (the thermal expansion difference between stainless steel and POM materials reaches 2.3×10⁻ 5 / °C) and mechanical wear, the actual clearance expands to 0.15 - 0.25 mm. This clearance causes the following problems: The reaction liquid seeps into the clearance and solidifies to form a burr with a width of 0.1 - 0.3 mm (measurement data by a laser confocal microscope), and additional manual trimming is required, increasing the single-piece processing cost by 15% The aldehyde cross-linking agent crystallizes at the clearance to generate sulfate particles with a particle size of 5 - 10 μm (confirmed by SEM-EDS detection), contaminating the surface of the cleaning brush, and causing 18.5% of the products to be judged as defective due to foreign matter residues Performance deterioration caused by untreated bubbles: The gas content of the PVA reaction liquid without degassing is as high as 3.5 - 4.8 vol% (tested according to the GB / T 6287 standard), and two types of defects are formed after curing: Macroscopic bubbles: Bubbles with a diameter > 50 μm burst on the surface of the bristles, generating pits with a depth > 30 μm (measurement data by a white light interferometer), resulting in a 40% increase in the probability of bristle breakage during the cleaning process Microscopic pores: Closed pores with a diameter of 10 - 30 μm (confirmed by μCT three-dimensional reconstruction) reduce the effective specific surface area of the brush body by 32%, directly weakening the intensity of the cavitation effect during ultrasonic cleaning (the measured cleaning efficiency drops by 28%) Structural scrap caused by incomplete filling of high-viscosity fluid: The dynamic viscosity of the PVA solution reaches 2,500 - 3,500 mPa·s at 50°C (tested by a Brookfield DV2T viscometer), and the filling rate of the brush pore channels with a diameter < 0.3 mm by the traditional gravity injection molding process is only 78 - 82% (data recorded by high-speed photography). Two types of defects occur in the unfilled pore channels during the foaming stage: Top voids: An unfrothed area with a diameter of 0.5 - 1.2 mm is formed at the upper part of the pore diameter (analysis result of metallographic section), resulting in 22% of the products being scrapped due to missing bristles Gradient density anomaly: The difference in foaming density between the bottom and the top of the pore is > 15% (measured data by a densitometer). When the brush body is compressed, local collapse occurs, and the dynamic compression resilience (tested by ASTM D395) decreases from 1.5 MPa to 0.9 MPa. Summary of the Invention

[0003] To solve the above problems, the present invention provides a preparation method for a high-elastic PVA cleaning brush without burrs, which solves the problems of low product yield and high production cost. The method of the present invention includes the following steps: (1) Mold pretreatment: Wrap the outside of the mold with an FEP heat-shrinkable film, and through high-temperature treatment, make the FEP heat-shrinkable film shrink and tightly wrap the mold to complete the assembly combination of the mold end cover and the shaft core. The gap between the FEP heat-shrinkable film and the mold is less than 0.01 mm; (2) Solution preparation: Heat and dissolve polyvinyl alcohol in a reaction kettle to form an aqueous solution, and sequentially add starch with a particle size of more than 50 mesh, an aldehyde cross-linking agent, an acidic catalyst, and an antifoaming agent, and stir evenly to obtain a mixed solution; (3) Defoaming treatment: Perform vacuum pumping on the mixed solution obtained in step (2) to remove the bubbles in the solution; (4) Injection molding: Inject the defoamed solution into the combined mold, and install the end cover after the injection is completed; (5) Centrifugal treatment: Centrifuge the injection mold at a speed of 100 - 500 revolutions per minute for 30 seconds to remove the void bubbles in the upper part of the holes; (6) Foaming and shaping: Place the mold in an oven for staged foaming treatment to form a sponge substrate. The staged foaming time and temperature are respectively: the first stage: 30 °C, 60 min; the second stage 30 °C - 40 °C, 30 min; the third stage 40 °C, 120 min; the fourth stage 40 °C - 50 °C, 30 min; the fifth stage 50 °C, 120 min; the sixth stage 50 °C - 60 °C, 30 min; the seventh stage 60 °C, 120 min; the eighth stage 60 °C - 70 °C, 30 min; the ninth stage 70 °C, 120 min; (7) Post-treatment: Take out the sponge substrate, wash it with water to remove starch, and obtain the final product after cutting off the excess part.

[0004] Further, in step (2) of the present invention, the aldehyde cross-linking agent is formaldehyde, the acidic catalyst is sulfuric acid, and the antifoaming agent is selected from at least one of ether compounds or silicon compounds.

[0005] Further, in step (5) of the present invention, the centrifugal treatment adopts a stepped speed control, with an initial speed of 100 revolutions per minute and a final speed reaching 500 revolutions per minute.

[0006] Further, in step (6) of the present invention, the foaming treatment adopts a gradient temperature rising program. After maintaining the initial temperature of 30°C for 10 - 15 minutes, the temperature is raised to 80°C at a rate of 1 - 2°C / min.

[0007] Further, in step (2) of the present invention, the starch addition amount is 20 - 35% of the mass of polyvinyl alcohol, and the aldehyde cross - linker addition amount is 0.5 - 2% of the mass of polyvinyl alcohol.

[0008] Further, in step (3) of the present invention, during the vacuum treatment, the vacuum degree is maintained at - 0.08~ - 0.1MPa, and the treatment time is 15 - 30 minutes.

[0009] Further, in step (7) of the present invention, the water washing treatment adopts a circulating water flushing process. The water temperature is controlled at 25 - 40°C, and the flushing time is 30 - 60 minutes.

[0010] Further, the shrinkage temperature of the FEP heat - shrinkable film of the present invention is 120 - 150°C, and the shrinkage rate is 30 - 50%.

[0011] Compared with the prior art, the preparation method of a non - burr high - elastic PVA cleaning brush of the present invention has the following technical effects: 1. Revolutionary improvement in mold sealing: Through the innovative process of directly shrinking and wrapping the mold with an FEP heat - shrinkable film, the assembly gap of the traditional sleeve mold of 0.1 - 0.3mm is reduced to less than 0.01mm, effectively preventing burrs and liquid overflow. The defective rate of the product appearance is reduced from the industry average of 15% to less than 2%. 2. Dual guarantee for bubble control: Adopting the synergistic treatment technology of adding defoamers (silicone / ether type) and vacuum degassing (- 0.08~ - 0.1MPa), the gas content in the reaction liquid is reduced from 3 - 5vol% in the conventional process to less than 0.5vol%, eliminating more than 90% of the void defects. 3. Breakthrough in fluid filling optimization: The unique centrifugal treatment process (100 - 500rpm, 30s) compensates for the fluidity defects of high - viscosity solutions (2000 - 5000cps) through centrifugal force, making the filling integrity of the internal holes of the mold reach 99.8%, and the surface roughness Ra of the foamed product ≤6.3μm. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention. In the drawings: Figure 1 A non - burr high - elastic PVA cleaning brush prepared by the method of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0013] To make the objectives, technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with specific embodiments of the present invention and the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without any creative work belong to the scope of protection of the present invention.

[0014] A preparation method of a hairless and highly elastic PVA cleaning brush of the present invention comprises the following steps: (1) Mold pretreatment: Wrap an FEP heat-shrinkable film around the outside of the mold, and through high-temperature treatment, make the FEP heat-shrinkable film shrink and tightly wrap the mold to complete the assembly combination of the mold end cover and the shaft core; the shrinkage temperature is 120 - 150 °C, the shrinkage rate is 30 - 50%, the FEP heat-shrinkable film hardly reacts with any chemical substances, can withstand the erosion of strong acids (such as sulfuric acid, nitric acid), strong alkalis, strong oxidants and organic solvents (such as ketones, esters), the shrinkage rate reaches 30% at a temperature above 200 °C, and the gap between the heat-shrinkable film and the mold is less than 0.01 mm, ensuring that the reaction solution will not penetrate into the gap between the heat-shrinkable film and the mold.

[0015] (2) Solution preparation: Heat and dissolve polyvinyl alcohol in a reaction kettle to form an aqueous solution, and sequentially add starch with a particle size of more than 50 mesh, an aldehyde cross-linking agent, an acidic catalyst and an antifoaming agent, and stir evenly to obtain a mixed solution; the aldehyde cross-linking agent is formaldehyde, the acidic catalyst is sulfuric acid, and the antifoaming agent is selected from at least one of ether compounds or silicon compounds. The addition amount of starch is 20 - 35% of the mass of polyvinyl alcohol, and the addition amount of the aldehyde cross-linking agent is 0.5 - 2% of the mass of polyvinyl alcohol. Polyvinyl alcohol is the basic material of the sponge. Its molecular chain contains a large number of hydroxyl groups (-OH), forming a hydrogen bond network, providing good film-forming properties and mechanical strength, and can also endow the sponge with excellent water absorption and water retention properties, and is widely used in fields such as cleaning and medical treatment. As a natural polymer, starch particles are dispersed in the PVA matrix, reducing costs and improving the flexibility of the sponge. The hydroxyl groups in starch can undergo cross-linking reactions with PVA and formaldehyde, enhancing the network structure. Sulfuric acid, as a catalyst, provides an acidic environment, catalyzes the condensation reaction (forming ether bonds) of the hydroxyl groups in PVA and starch with formaldehyde, promotes the rapid formation of the cross-linking network, and indirectly regulates the pore size and density of the sponge by controlling the reaction rate and affecting the generation and stability of bubbles. Formaldehyde, as a cross-linking agent, can undergo acetalization reactions with the hydroxyl groups of PVA / starch to form -CH2-O-CH2- bridge bonds, greatly improving the water resistance, mechanical strength and heat resistance of the sponge. The cross-linking network prevents PVA from dissolving in water, enabling the sponge to maintain its shape and be reused.

[0016] (3)Defoaming treatment: The mixed solution obtained in step (2) is subjected to vacuum treatment to remove the air bubbles in the solution; during the vacuum treatment, the vacuum degree is maintained at -0.08 to -0.1 MPa, and the treatment time is 15 - 30 minutes.

[0017] (4)Injection molding: Inject the defoamed solution into the combined mold, and install the upper end cover after the injection is completed; (5)Centrifugal treatment: Centrifuge the injection mold at a speed of 100 - 500 revolutions per minute for 30 seconds to remove the void bubbles in the upper part of the hole; the centrifugal treatment adopts stepped speed control, with an initial speed of 100 revolutions per minute and a final speed reaching 500 revolutions per minute.

[0018] (6)Foaming and shaping: Place the mold in an oven for staged foaming treatment to form a sponge base material; the foaming treatment adopts a gradient heating program, and the staged foaming time and temperature are respectively: the first stage: 30°C, 60 min; the second stage 30°C - 40°C, 30 min; the third stage 40°C, 120 min; the fourth stage 40°C - 50°C, 30 min; the fifth stage 50°C, 120 min; the sixth stage 50°C - 60°C, 30 min; the seventh stage 60°C, 120 min; the eighth stage 60°C - 70°C, 30 min; the ninth stage 70°C, 120 min.

[0019] (7)Post-treatment: Take out the sponge base material and wash it with water to remove the starch, and obtain the final product after cutting off the excess part. The water washing treatment adopts a circulating water flushing process, with the water temperature controlled at 25 - 40°C and the flushing time of 30 - 60 minutes.

[0020] The technical solutions provided by each embodiment of the present invention are described in detail below.

[0021] Example 1 (1)Mold pretreatment: Select a PETFEP heat-shrinkable film (shrinkage rate 40%), place the mold in a hot air oven at 130°C for 3 minutes to make the FEP heat-shrinkable film completely wrap the working surface of the mold, and the measured assembly gap of the mold ≤ 0.008 mm.

[0022] (2)Solution preparation: Add 10 kg of polyvinyl alcohol (PVA1788) to the reaction kettle, heat it to 90°C and dissolve it, then add 2.5 kg of 60-mesh tapioca starch, 0.1 kg of formaldehyde (37% aqueous solution), 0.08 kg of concentrated sulfuric acid (98%), and 0.05 kg of polyether-modified silicone oil defoamer in sequence, and stir at 800 rpm for 30 minutes.

[0023] (3)Defoaming treatment: Transfer the mixed solution to a vacuum defoaming tank, and treat it at a vacuum degree of -0.09 MPa for 20 minutes, and the measured gas content in the solution is 0.3 vol%.

[0024] (4) Injection molding: Use a high-pressure liquid injection machine (pressure 0.5 MPa) to inject the solution into the mold, and control the injection time within 45 seconds to complete.

[0025] (5) Centrifugation: Adopt a three-stage centrifugation program (100 rpm × 10 s → 300 rpm × 10 s → 500 rpm × 10 s), and the total processing time is 30 seconds.

[0026] (6) Foaming and shaping: Place the mold in an oven for staged foaming treatment to form a sponge substrate. The staged foaming time and temperature are as follows: the first stage: 30 °C, 60 min; the second stage 30 °C - 40 °C, 30 min; the third stage 40 °C, 120 min; the fourth stage 40 °C - 50 °C, 30 min; the fifth stage 50 °C, 120 min; the sixth stage 50 °C - 60 °C, 30 min; the seventh stage 60 °C, 120 min; the eighth stage 60 °C - 70 °C, 30 min; the ninth stage 70 °C, 120 min.

[0027] (7) Post-treatment: Rinse with 35 °C circulating water for 45 minutes to remove starch, and obtain a sponge product with a dimensional tolerance of ±0.1 mm after cutting as Figure 1 shown.

[0028] Example 2 (1) Mold pretreatment: Use a PVCFEP heat-shrinkable film (shrinkage rate 35%) to treat at 140 °C for 5 minutes.

[0029] (2) Solution preparation: The PVA addition amount is 8 kg, the starch addition ratio is increased to 28% (2.24 kg), and the formaldehyde addition amount is 1.5% (0.12 kg).

[0030] (3) Defoaming treatment: Increase the vacuum degree to -0.1 MPa and treat for 25 minutes.

[0031] (5) Centrifugation: Adopt a linear speed increase mode (continuously adjusted from 100 - 500 rpm).

[0032] (6) The foaming program is adjusted to 30 °C × 15 min → Gradually increase the temperature to 75 °C.

[0033] The remaining steps are the same as in Example 1 Perform performance tests on the sponge products prepared in Examples 1 - 2, and the test results are as follows:

[0034] Through the synergistic effect of three core technologies, namely FEP heat shrinkable film sealing, vacuum degassing, and gradient centrifugation, the present invention increases the yield rate of sponge products by more than 20% and extends the die life by 4-5 times. In particular, it meets the medical device grade standards in terms of pore size uniformity (CV value ≤ 3%) and surface finish (Ra ≤ 5μm).

[0035] The above are only examples of the present invention and are not intended to limit the present invention. For those skilled in the art, various changes and modifications can be made to the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the scope of the claims of the present invention.

Claims

1. A preparation method of a high-elastic PVA cleaning brush without burrs, characterized in that, It includes the following steps: (1) Mold pretreatment: Wrap the outer side of the mold with an FEP heat-shrinkable film, and through high-temperature treatment, make the FEP heat-shrinkable film shrink and tightly wrap the mold to complete the assembly combination of the mold end cover and the shaft core. The gap between the FEP heat-shrinkable film and the mold is less than 0.01 mm; (2) Solution preparation: Heat and dissolve polyvinyl alcohol in a reaction kettle to form an aqueous solution, and successively add starch with a particle size of more than 50 mesh, an aldehyde cross-linking agent, an acidic catalyst, and an antifoaming agent. After stirring evenly, a mixed solution is obtained; (3) Defoaming treatment: Perform vacuum pumping on the mixed solution obtained in step (2) to remove the air bubbles in the solution; (4) Injection molding: Inject the defoamed solution into the combined mold, and install the end cover after the injection is completed; (5) Centrifugal treatment: Centrifuge the injection mold at a speed of 100 - 500 revolutions per minute for 30 seconds to remove the void bubbles in the upper part of the hole; (6) Foaming and shaping: Place the mold in an oven for staged foaming treatment to form a sponge substrate. The staged foaming time and temperature are respectively: the first stage: 30 °C, 60 min; the second stage 30 °C - 40 °C, 30 min; the third stage 40 °C, 120 min; the fourth stage 40 °C - 50 °C, 30 min; the fifth stage 50 °C, 120 min; the sixth stage 50 °C - 60 °C, 30 min; the seventh stage 60 °C, 120 min; the eighth stage 60 °C - 70 °C, 30 min; the ninth stage 70 °C, 120 min; (7) Post-treatment: Take out the sponge substrate and wash it with water to remove the starch, and obtain the final product after cutting off the excess part.

2. The preparation method according to claim 1, characterized in that: In step (2), the aldehyde cross-linking agent is formaldehyde, the acidic catalyst is sulfuric acid, and the antifoaming agent is selected from at least one of ether compounds or silicone compounds.

3. The preparation method according to claim 1, characterized in that: In step (5), the centrifugal treatment adopts stepped speed control, with an initial speed of 100 revolutions per minute and a final speed reaching 500 revolutions per minute.

4. The preparation method according to claim 1, wherein: In step (6), the foaming treatment adopts a gradient heating program. After maintaining the initial temperature of 30 °C for 10 - 15 minutes, the temperature is raised to 80 °C at a rate of 1 - 2 °C / min.

5. The preparation method according to claim 1, wherein: In step (2), the starch addition amount is 20 - 35% of the mass of polyvinyl alcohol, and the aldehyde cross-linking agent addition amount is 0.5 - 2% of the mass of polyvinyl alcohol.

6. The preparation method according to claim 1, wherein: When performing the vacuum pumping treatment in step (3), the vacuum degree is maintained at -0.08~-0.1 MPa, and the treatment time is 15 - 30 minutes.

7. The preparation method according to claim 1, characterized in that: In step (7), the water washing treatment adopts a circulating water flushing process, the water temperature is controlled at 25 - 40 °C, and the flushing time is 30 - 60 minutes.

8. The preparation method according to claim 1, wherein: The shrinking temperature of the FEP heat-shrinkable film is 120 - 150 °C, and the shrinkage rate is 30 - 50%.

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