Contact lens mold injection molding process

Abstract

The invention discloses a contact lens mold injection molding process, and relates to the technical field of contact lens manufacturing, and the contact lens mold injection molding process comprises the following steps: S1, raw material dehumidification and drying treatment; s2, preheating the raw materials; s3, homogenizing the raw materials; s4, during injection molding, a filling mode with the injection speed being 10-20 cm < 3 > / s is adopted in the 0%-20% stage; a filling mode with the injection speed of 30-50 cm < 3 > / s is adopted in the 20%-85% stage; the remaining space is filled in a micro pulse type injection mode; s5, the mold is placed in a pressurizing bin, and the materials are pressurized and cured; and S6, demolding is conducted, specifically, a vacuum adsorption module is arranged on the surface of the mold, the surface of the mold is adsorbed, and compressed air is injected into the mold through a gas-assisted demolding module to assist demolding. Through mold structure optimization, the service life of the mold is prolonged, the forming quality of a product is improved, product defects are reduced, and especially for contact lens molds, the high-precision requirement of the contact lens molds can be guaranteed, and the strict standard of contact lens production is met.

Description

Technical Field

[0001] The invention relates to the technical field of contact lens manufacturing, in particular to a contact lens mold injection molding process. Background Art

[0002] With the rapid development of the times, people's lives are becoming more and more diversified, and people's pursuit of beauty and fashion is also changing with each passing day. In recent years, young women have been increasingly pursuing contact lenses and cosmetic lenses, which has greatly promoted the vigorous development of the contact lens industry. As a result, the production process of contact lenses has been continuously updated and upgraded. From the traditional turning molding process to the current centrifugal molding method and compression molding method, each manufacturer chooses a production process that suits them according to their own needs and technical mastery level.

[0003] In the traditional turning and molding process, turning and polishing are indispensable. However, due to the existence of these two processes, the various processes of the contact lens production process, from the molding process to the demolding process, are separated from each other. This not only makes it impossible to achieve fully automatic production of contact lenses, consuming a large amount of human resources and equipment resources, but also the lenses produced are prone to bright spots, threads, scratches, photometric errors, thickness errors and other unqualified phenomena, thus affecting the production efficiency and quality of contact lenses. Moreover, according to market feedback, the comfort of lenses produced by the turning molding process is not ideal, and they are not suitable as short-cycle disposable lenses.

[0004] In order to solve the problems caused by the turning process, more advanced production processes have been developed, such as centrifugal molding, compression molding, etc. Among them, compression molding is currently the most widely used. Compression molding is also called casting molding. Its process flow is: first use a mold injection molding machine to make an upper mold (convex mold) and a lower mold (concave mold) with set parameters, then inject the liquid lens material into the concave mold, and then embed the convex mold into the concave mold and press it to form a mold composition, and then heat or irradiate the mold composition with ultraviolet light to solidify it, and finally demold it to obtain the desired lens. Compression molding is not only efficient, simple to operate, quality controllable, and low cost, but also the lenses produced by this method are soft and comfortable to wear, suitable as short-cycle disposable lenses. After years of development, the contact lenses on the market are showing a phenomenon that the shorter the disposal cycle, the more popular they are with consumers. This requires manufacturers to have strong lens production capabilities, so advanced compression molding production technology has become a decisive factor in the competition among manufacturers.

[0005] However, there are many problems with the traditional injection molding process. For example, the temperature and pressure control during the injection molding process is not precise enough, resulting in defects such as shrinkage marks, deformation, and bubbles in the product, which affects the accuracy of the contact lens mold and the sealing and appearance quality of the PP box. Summary of the Invention

[0006] The object of the present invention is to solve the defects existing in the prior art, and a process for injection molding of contact lens molds is proposed.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] A process for injection molding of contact lens molds includes the following steps:

[0009] S1: Raw material dehumidification and drying treatment: For the pretreatment of raw materials, the raw material particles are placed in a vacuum dehumidification and drying equipment equipped with a molecular sieve rotor for dehumidification and drying treatment;

[0010] S2: Raw material preheating treatment: The dried raw materials are introduced into a spiral preheating device for preheating treatment;

[0011] S3: Raw material homogenization treatment: The preheated raw materials are introduced into a double planetary mixer to mix the materials and then transported to an injection molding machine;

[0012] S4: During injection molding, a filling method with an injection speed of 10 - 20 cm 3 / s is adopted in the 0% - 20% stage; a filling method with an injection speed of 30 - 50 cm 3 / s is adopted in the 20% - 85% stage; the remaining space adopts a micro-pulse injection method to complete filling;

[0013] S5: Place the mold in a pressurized chamber to pressurize and cure the material;

[0014] S6: Demolding: A vacuum adsorption module is set on the surface of the mold to adsorb the surface of the mold, and then a gas-assisted demolding module is used to inject compressed air into the mold to assist in demolding.

[0015] Further, it also includes step S7: Post-injection treatment. The product first enters a liquid nitrogen spray cooling tunnel for cooling, and then is transferred to a hot pressing and shaping device to be kept under pressure for 2 - 5 minutes at 50 - 70°C and 1 - 2 MPa to eliminate internal residual stress.

[0016] Further, it also includes step S8: Surface optimization treatment. For the formed contact lenses, a nano-coating spraying process is adopted to form a hydrophobic layer with a thickness of 400 - 600 nm on the surface through electrostatic adsorption; and for the contact lens molds, additional magnetorheological polishing treatment is carried out.

[0017] Further, in step S1, the dehumidification and drying process is carried out relying on a vacuum dehumidification and drying equipment equipped with a molecular sieve rotor. The rotor is divided into three functional areas: an adsorption area, a desorption area, and a cooling area, and circulates at a constant speed of 8 - 12 revolutions per hour.

[0018] Further, in the step S2, the spiral preheating device has a double-layer sleeve structure, with the inner layer being the material conveying channel and the outer layer being the circulating heat-conducting oil heating chamber; the spiral conveying blades are designed with variable pitches, with a pitch of 80 mm at the feeding end and reduced to 50 mm at the discharging end.

[0019] Further, in the step S3, the double planetary mixer is equipped with two sets of planetary stirring paddles rotating in opposite directions, with a speed ratio of 1:1.5, and the surfaces of the stirring paddles are coated with Teflon; the ends of the paddle blades are designed with serrated structures.

[0020] Further, in the step S6, a flexible ejection module is further included, and the flexible ejection module adopts an elastic rubber ejector rod structure.

[0021] Advantages

[0022] Compared with the prior art, the advantages of the present invention are as follows:

[0023] Through the optimization of the mold structure, the service life of the mold and the forming quality of the product are improved, product defects are reduced. Especially for contact lens molds, their high-precision requirements can be guaranteed, meeting the strict standards for contact lens production.

[0024] The precise control of injection parameters and the innovation of the process flow effectively improve the production efficiency, shorten the production cycle of the product, and reduce the production cost. For example, after adopting conformal cooling channels and segmented injection processes, the cooling time can be shortened by 30%-50%, and the production efficiency can be increased by 20%-30%.

[0025] The improvement of the demolding process reduces the damage to the product during demolding, improves the qualified rate of the product. At the same time, the automatic detection device ensures the cleanliness of the mold and the continuity of production.

[0026] The special treatment of raw materials and the rapid cooling and shaping of the product improve the dimensional stability and surface quality of the product, making the PP box have better sealing performance and appearance effect, and enhancing the market competitiveness of the product. Description of the Drawings

[0027] The drawings are used to provide a further understanding of the present invention, and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention, and do not constitute a limitation to the present invention.

[0028] Figure 1 It is a process flow schematic diagram of an injection molding process for a contact lens mold. Detailed Embodiments

[0029] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments.

[0030] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by the terms "upper", "lower", "front", "rear", "left", "right", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the accompanying drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention.

[0031] Embodiment 1:

[0032] An injection molding process for a contact lens mold includes the following steps:

[0033] S1: Raw material dehumidification and drying treatment: For the pretreatment of raw materials, the raw material particles are placed in a vacuum dehumidification and drying device equipped with a molecular sieve rotor for dehumidification and drying treatment;

[0034] S2: Raw material preheating treatment: The dried raw materials are introduced into a spiral preheating device for preheating treatment;

[0035] S3: Raw material homogenization treatment: The preheated materials are introduced into a double planetary mixer to mix the materials and then transported to an injection molding machine;

[0036] S4: During injection molding, a filling method with an injection speed of 10 - 20 cm 3 / s is adopted in the 0% - 20% stage; a filling method with an injection speed of 30 - 50 cm 3 / s is adopted in the 20% - 85% stage; the remaining space adopts a micro pulse injection method to complete filling;

[0037] S5: Place the mold in a pressurized chamber to pressurize and cure the material;

[0038] S6: Demolding: A vacuum adsorption module is set on the mold surface to adsorb the mold surface, and then a gas-assisted demolding module is used to inject compressed air into the mold to assist in demolding.

[0039] Furthermore, it also includes step S7: Post-injection molding treatment. The product first enters a liquid nitrogen spray cooling tunnel for cooling, and then is transferred to a hot pressing and shaping device to be kept under pressure for 2 - 5 minutes at 50 - 70 °C and 1 - 2 MPa to eliminate internal residual stress.

[0040] Further, it also includes step S8: surface optimization treatment. For the formed contact lenses, a nano - coating spraying process is adopted, and a hydrophobic layer with a thickness of 400 - 600 nm is formed on the surface through electrostatic adsorption; and for the contact lens mold, magnetorheological polishing treatment is additionally carried out.

[0041] Further, in step S1, the dehumidification and drying process is carried out relying on a vacuum dehumidification and drying device equipped with a molecular sieve rotor. The rotor is divided into three functional areas: an adsorption area, a desorption area, and a cooling area, and operates in a constant - speed cycle at 8 - 12 revolutions per hour.

[0042] Further, in step S2, the spiral pre - heating device has a double - layer sleeve structure. The inner layer is a material conveying channel, and the outer layer is a circulating heat - conducting oil heating cavity; the spiral conveying blades adopt a variable pitch design, with a pitch of 80 mm at the feeding end and reduced to 50 mm at the discharging end.

[0043] Further, in step S3, the double - planetary mixer is equipped with two sets of reversely rotating planetary stirring paddles, with a speed ratio of 1:1.5. The surface of the stirring paddles is coated with a Teflon coating; the ends of the paddle blades are designed with a serrated structure.

[0044] Further, in step S6, it also includes a flexible ejection module, and the flexible ejection module adopts an elastic rubber ejector rod structure.

[0045] Example 2: Refer to Figure 1 ,

[0046] I. Pretreatment of raw materials before injection molding

[0047] For the pretreatment of raw materials, a three - stage treatment process system of dehumidification drying - preheating - homogenization is adopted. First, the raw material particles are placed in a vacuum dehumidification and drying device equipped with a molecular sieve rotor and processed within the temperature range of 100 - 120 °C for 4 - 6 hours. This device accelerates the vaporization of raw material moisture through the synergistic effect of a hot - air circulation system and a vacuum environment. After strict control, the moisture content of the raw materials is stably below 0.02%, effectively eliminating the root cause of bubble defects in the injection - molding process. After the dehumidification process is completed, the raw material particles are gradually heated to 60 - 80 °C using a spiral pre - heating device, and uniform heat conduction of the materials is achieved through the built - in stirring system, significantly reducing the melt viscosity. To ensure the batch stability of raw material quality, after each batch of treatment, sampling inspection is carried out using an infrared moisture detector, and a complete quality traceability file is established to record the test data in detail.

[0048] 1. Dehumidification drying

[0049] The dehumidification and drying process is carried out relying on a vacuum dehumidification and drying device equipped with a molecular sieve rotor. The molecular sieve rotor of this device uses a honeycomb - shaped ceramic substrate, and the surface is loaded with a composite adsorbent of activated silica gel and alumina, forming a specific surface area of 800 - 1000 m 2High-efficiency adsorption structure per gram. The rotating wheel is divided into three functional areas: the adsorption area, the desorption area, and the cooling area, and circulates at a constant speed of 8 - 12 revolutions per hour.

[0050] In the adsorption area, the raw material particles are in full contact with the preheated dry hot air. The hot air is heated by an electric heating device to 120 - 140 °C and penetrates the material layer at a flow rate of 0.5 - 0.8 m / s, vaporizing the moisture on and inside the particle surface. At the same time, the molecular sieve rotating wheel adsorbs the moisture in the air, making the dew point temperature of the air entering the material area as low as -40 °C, ensuring the efficient progress of the drying process.

[0051] When the rotating wheel rotates to the desorption area, it is purged reversely by high-temperature hot air at 180 - 200 °C, so that the adsorbent desorbs moisture and restores its activity; then it is cooled by normal-temperature air in the cooling area and re-enters the adsorption cycle.

[0052] The raw material particles are treated in the temperature range of 100 - 120 °C for 4 - 6 hours. This parameter setting is based on the thermal stability of the PP material and the moisture vaporization kinetics characteristics. Through experimental verification, within this temperature range, it can not only ensure that the raw material particles will not degrade due to overheating, but also make the moisture vaporization rate reach the optimal state. The built-in vacuum system of the equipment can maintain the chamber pressure at 5 - 10 kPa, further reducing the boiling point of water, and cooperating with the hot air circulation system, stably controlling the moisture content of the raw material below 0.02%.

[0053] It should be noted that the system is also equipped with a dynamic humidity monitoring device, which real-time feeds back the moisture content of the material through a capacitive humidity sensor. Once an abnormality is detected, it will automatically extend the drying time or adjust the hot air temperature to ensure that the drying effect meets the standard.

[0054] 2. Preheating process

[0055] The preheating process uses a spiral preheating device, which consists of a double-layer sleeve structure. The inner layer is the material conveying channel, and the outer layer is the circulating heat-conducting oil heating chamber. The spiral conveying blades adopt a variable pitch design. The pitch at the feeding end is 80 mm, and the pitch at the discharging end is reduced to 50 mm, so that the material is gradually compacted during the conveying process, enhancing the heat conduction efficiency. The surface of the conveying shaft is provided with fine grooves, which cooperate with the built-in stirring blades to achieve 360° flipping of the material, ensuring that each raw material particle can be evenly heated.

[0056] The circulating heat transfer oil heating chamber gradually heats the raw material particles to 60-80°C. According to tests, at this temperature, the melt flow rate (MFR) of PP can be increased by 20-30%, and the melt viscosity can be reduced by about 15-20%, which effectively improves the fluidity of the material. During the preheating process, the temperature of the heat transfer oil is precisely adjusted by the PID temperature control system with a control accuracy of ±0.5°C. The device is also equipped with an infrared temperature measurement array to monitor the material temperature at multiple points in real time, and adjust the heat transfer oil flow rate through feedback control to ensure that the discharge temperature fluctuation range does not exceed ±1°C. In addition, a vibration screening device is set at the discharge port to screen out particles that are stuck due to local overheating, further ensuring the quality of the material.

[0057] 3. Homogenization process

[0058] As the key finishing step of the three-stage treatment system, the homogenization stage uses a double planetary mixer to achieve fine mixing of materials. The mixer is equipped with two sets of counter-rotating planetary impellers with a speed ratio of 1:1.5. Under the combined motion of revolution and rotation, strong shear and convection effects can be generated. The surface of the impeller is coated with Teflon coating to prevent material adhesion, and the end of the impeller is designed with a serrated structure to effectively break up lumps in the material.

[0059] During the homogenization process, the mixer runs at a speed of 60-80rpm for 15-20 minutes to fully mix the raw material particles from different batches and different regions to achieve a high degree of uniformity in density, humidity and temperature. To ensure the homogenization effect, the system introduces a near-infrared spectroscopy online analyzer to detect the uniformity of the material composition in real time. When it is detected that the composition deviation exceeds the set threshold, the stirring time is automatically extended or the secondary homogenization program is started. After the homogenization is completed, the material is directly transported to the injection molding machine hopper through a closed pipe to avoid secondary contamination.

[0060] 2. Injection molding process control

[0061] The injection stage adopts a three-stage precise injection curve, which fully considers the different molding requirements of contact lens molds and PP boxes and is designed in combination with the flow characteristics of the melt in the mold cavity.

[0062] Initial low-speed filling stage: set the injection speed to 10-20cm 3 / s, this stage is designed to avoid bubbles and trapped air caused by turbulence in the melt during high-speed injection. Combined with the unique spoiler groove design on the mold surface, these spoiler grooves are distributed in a spiral or radial pattern, which can guide the melt entering the mold cavity and guide the melt to move forward smoothly and orderly. Taking the contact lens mold as an example, low-speed filling can make the melt spread slowly in the mold cavity, reducing mold damage caused by melt impact, while ensuring that the fine structure of the mold cavity can be accurately filled with the melt, ensuring the high-precision requirements of the contact lens mold.

[0063] Mid - stage speed - up filling stage: Increase the injection speed to 30 - 50 cm 3 / s, and quickly complete about 80% of the filling volume of the mold cavity. In this stage, by accelerating the melt flow, while ensuring good melt fluidity, the production efficiency is improved. For PP boxes, rapid filling can make the melt temperature and pressure distribution in each part of the box body relatively uniform, reduce the problem of uneven melt cooling caused by too long filling time, and avoid local sink marks or warping deformation.

[0064] End - stage micro - pulse injection stage: Adopt the micro - pulse injection method. Through high - frequency and small - dose melt injection, the weld line defect is eliminated. When the mold cavity is nearly full, the flow resistance of the melt increases, and it is easy to form a weld line at the confluence of two melt streams. Micro - pulse injection can make the melt at the confluence fully fuse. By adjusting the frequency of the pulse and the volume of the melt injected each time, the appearance and strength of the weld line can be effectively improved. For example, for PP boxes with transparent appearance requirements, in this stage, the weld line can be almost invisible, improving the appearance quality and performance of the product.

[0065] III. Curing process

[0066] Apply a certain pressure during the polypropylene molding process to help the molecular chains arrange and crystallize better, improving the density and strength of the product. It can be used in combination with thermal curing. While heating, apply pressure to promote the acceleration of polypropylene curing under the action of pressure. When pressing polypropylene plates or profiles, the method of heating and pressurizing is often adopted to make the polypropylene raw material flow and cure fully under high temperature and high pressure, obtaining products with excellent performance.

[0067] IV. Demolding process

[0068] The innovatively designed vacuum - assisted composite demolding system consists of three core functional modules:

[0069] Vacuum adsorption module: Construct a 0.3 - mm precision micro - pore array on the mold forming surface, and achieve uniform adsorption and positioning of the product through a 95 - kPa negative pressure field;

[0070] Gas - assisted demolding module: Arrange gas needle assemblies at key positions on the edge of the product, and use 6 - 8 bar compressed air to form a gas film layer, effectively reducing the demolding resistance;

[0071] Flexible ejection module: Adopt an elastic rubber ejector rod structure to avoid damage to the product surface caused by rigid contact.

[0072] In other preferred embodiments, for the quality control of contact lens molds, a line-scan machine vision inspection system can be configured. This system has a super-high resolution scanning ability of 2000 dpi. Relying on a feature database containing more than 5000 types of defect samples, it can accurately identify foreign objects at the 0.01 mm level. The inspection data is uploaded to the Manufacturing Execution System (MES) in real time. Once the abnormal judgment mechanism is triggered, the mold cleaning process is immediately started, and the surface cleaning treatment is completed through the coordinated operation of a high-pressure ion air gun and an ultrasonic cleaning device.

[0073] V. Post-processing after injection molding

[0074] Construct a post-processing system for gradient cooling - stress elimination - surface optimization. The product first enters a liquid nitrogen spray cooling tunnel for cooling to form a dense crystal structure. Subsequently, it is transferred to a hot pressing and shaping device, where it is kept under pressure at 60 °C and 1.5 MPa for 3 minutes to eliminate internal residual stress. For the PP box, a nano-coating spraying process is adopted, and a 500-nm-thick hydrophobic layer is formed on the surface through electrostatic adsorption, increasing the surface tension from 42 mN / m to 75 mN / m and significantly enhancing the sealing performance. The contact lens mold is additionally subjected to magnetorheological polishing treatment, using a magnetic field to control the rheological properties of the polishing liquid to achieve a mirror finish with Ra 0.05 μm, ensuring that the surface roughness of the mold meets the optical grade standard.

[0075] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution of the present invention and its inventive concept, makes equivalent substitutions or changes, and should be covered by the protection scope of the present invention.

Claims

1. An injection molding process for a contact lens mold, characterized in that, It includes the following steps: S1: Pretreatment of raw materials for dehumidification and drying: For the pretreatment of raw materials, place the raw material particles in a vacuum dehumidification and drying equipment equipped with a molecular sieve rotary wheel for dehumidification and drying treatment; S2: Preheating treatment of raw materials: Introduce the dried raw materials into a spiral preheating device for preheating treatment; S3: Homogenization treatment of raw materials: Introduce the preheated materials into a double planetary mixer to mix the materials and then transport them to an injection molding machine; S4: During injection molding, a filling method with an injection speed of 10 - 20 cm 3 / s is adopted in the 0% - 20% stage; a filling method with an injection speed of 30 - 50 cm 3 / s is adopted in the 20% - 85% stage; the remaining space is filled by a micro pulse injection method to complete the filling; S5: Place the mold in a pressurized chamber and pressurize and solidify the materials; S6: Demolding: Set a vacuum adsorption module on the surface of the mold to adsorb the surface of the mold, and then use a gas-assisted demolding module to inject compressed air into the mold to assist in demolding.

2. The injection molding process of a contact lens mold according to claim 1, wherein, It also includes step S7: Post-injection treatment. First, the product enters a liquid nitrogen spray cooling tunnel for cooling, and then is transferred to a hot pressing and shaping device. It is kept under pressure at 50 - 70 °C and 1 - 2 MPa for 2 - 5 minutes to eliminate internal residual stress.

3. A process for injection molding of a contact lens mold according to claim 1, characterized in that, It also includes step S8: Surface optimization treatment. For the formed contact lenses, a nano-coating spraying process is used to form a hydrophobic layer with a thickness of 400 - 600 nm on the surface through electrostatic adsorption; and the contact lens mold is additionally subjected to magnetorheological polishing treatment.

4. A process for injection molding of a contact lens mold according to claim 1, characterized in that, In step S1, the dehumidification and drying process is carried out relying on a vacuum dehumidification and drying equipment equipped with a molecular sieve rotary wheel. The rotary wheel is divided into three functional areas: an adsorption area, a desorption area, and a cooling area, and operates in a constant-speed cycle at 8 - 12 revolutions per hour.

5. A method for injection molding of a contact lens mold according to claim 1, characterized in that, In step S2, the spiral preheating device is a double-layer sleeve structure. The inner layer is a material transportation channel, and the outer layer is a circulating heat-conducting oil heating chamber; the spiral conveying blades adopt a variable pitch design, with a pitch of 80 mm at the feeding end and reduced to 50 mm at the discharging end.

6. A method for injection molding of a contact lens mold according to claim 1, characterized in that, In step S3, the double planetary mixer is equipped with two groups of reversely rotating planetary stirring paddles, with a speed ratio of 1:1.

5. The surface of the stirring paddles is coated with a Teflon coating; the ends of the paddle blades are designed with serrated structures.

7. A method for injection molding of a contact lens mold according to claim 1, characterized in that, In step S6, it also includes a flexible ejection module, and the flexible ejection module adopts an elastic rubber ejector rod structure.

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