Antistatic PBT contact lens mold and manufacturing method thereof

Abstract

The invention discloses an antistatic PBT (polybutylene terephthalate) contact lens mold and a manufacturing method thereof, and the antistatic PBT contact lens mold is prepared from the following components in parts by weight: 70-85 parts of PBT resin, 5 parts of PP (polypropylene) antistatic agent and 10-25 parts of modifier, the manufacturing method comprises the following steps: (1) preparing materials; (2) extruding and granulating; and (3) PBT mold injection molding. The PP antistatic agent is added into the formula of the PBT contact lens mold, so that the PBT mold can reduce impurity adhesion and prevent static accumulation, the demolding process of the lens is more convenient, and the yield and stability of the silicone hydrogel lens produced by full mold pressing can be obviously improved. Meanwhile, the PBT material is modified by adding the modifier, the PBT contact lens mold with good antistatic performance and mechanical performance is obtained by controlling rolling and injection molding parameters, the contact lenses are produced by adopting the PBT contact lens mold through a full mold pressing method, and the yield of the product can reach 96% or above.

Description

Technical Field

[0001] The invention relates to the technical field of contact lens preparation, and in particular to an antistatic PBT contact lens mold and a preparation method thereof. Background Art

[0002] Contact lenses, also known as corneal contact lenses, are transparent thin sheets placed on the surface of the cornea where vision deviation occurs to correct vision or protect the eyes. Currently, there are three main methods for making contact lenses: centrifugal casting, compression molding, and turning. Compression molding is to use metal molds to make polyester concave and convex molds according to standard sizes, and then use concave and convex molds to press them. It has the advantages of high processing efficiency, low cost, and good wearing comfort of the finished product. It is currently the processing technology used by most contact lens manufacturers.

[0003] In the process of preparing contact lenses by compression molding, the required raw materials are first mixed in proportion and quantitatively injected into the concave mold (PP mold), and then the convex mold (PBT mold) is placed in the concave mold for pressing. After the concave mold and the convex mold are engaged with each other, the material in the mold cavity is solidified to obtain the prefabricated shape of the contact lens. During the demolding process, the concave and convex mold combination is placed on a fixed frame, and the top of the combined mold is pressed with the help of a tool to separate the concave mold and the convex mold. After removing the redundant material on the edge, the lens attached to the convex mold is hydrated, and finally the finished lens is sterilized at high temperature, and a qualified product is obtained after passing the quality inspection.

[0004] The molding process is divided into half molding and full molding. At present, most contact lens manufacturers use full molding for production. In the full molding process, the PBT mold is combined with the PP mold, and the PBT mold and the PP mold are respectively given the base curved surface and the optical surface of the lens. Silicone hydrogel material has advantages in wearing comfort and other aspects, and is currently the mainstream material used in contact lens production. In the process of producing silicone hydrogel contact lenses by full molding, the PBT mold formula is composed of PBT, phenolic antioxidants and lubricants. Due to the soft material of the lens, the adhesion between the molds is strong, and demolding is difficult. The lens may crack during demolding, resulting in a low lens yield of only about 70%. Therefore, the full molding process of producing silicone hydrogel contact lenses must not only ensure the close fit of the upper and lower molds, but also consider the convenience of demolding. In the prior art, there are more improvements on the mold structure, demolding equipment and demolding methods, and there is no related report on improving the formula of the PBT mold itself to improve its electrostatic properties and thus improve the convenience of demolding. Summary of the invention

[0005] The invention aims to provide an antistatic PBT contact lens mold to improve the demoulding convenience of the contact lens, thereby improving the contact lens yield rate.

[0006] Another object of the present invention is to improve the method for making the above-mentioned antistatic PBT contact lens mold.

[0007] To achieve its purpose, the present invention adopts the following technical solution: The present invention provides a method for making an antistatic PBT contact lens mold. The formula of the antistatic PBT contact lens mold is as follows: 70-85 parts of PBT resin, 5 parts of PP antistatic agent, and 10-25 parts of modifier, in parts by weight. The method comprises the following steps: (1) Material preparation: Mix PBT resin, PP antistatic agent and modifier evenly according to the formula to obtain a mixed material for later use; (2) Extrusion granulation: The mixed material in step (1) is roll-milled on an extruder at a rolling temperature of 250-255° C. The modified PBT resin after roll milling is hot-cut granulated on the extrusion head of the extruder to obtain a granular PBT modified material, which is then dried for later use; (3) PBT mold injection: Install the injection mold on the mold frame of the precision injection molding machine and start the precision injection molding machine; pour the granular PBT modified material dried in step (2) into the material barrel. The injection molding conditions are as follows: Injection temperature 78~252℃, holding speed ≤20mm / s, injection pressure ≤700 kgf / cm 2 , injection time ≤ 2s, holding time ≤ 4s, cooling time ≤ 15s, injection molding and injection, to obtain a PBT contact lens mold.

[0008] As a further preferred embodiment of the technical solution of the present invention, the modifier is a mixture of acrylonitrile-butadiene-styrene terpolymer (ABS resin), polycarbonate (PC) and polyurethane elastomer (TPU).

[0009] Furthermore, the mixing mass of the ABS resin, PC and TPU is 1-5:1-3:1-2.

[0010] Furthermore, in step (2), the extruder is a twin-screw extruder, and the screw speed is 30-50 r / min; the rolling temperature in the first temperature section to the eighth temperature section is 250°C, and the rolling temperature in the ninth temperature section is 255°C.

[0011] Furthermore, in step (3), the precision injection molding machine has a five-stage temperature-controlled melt injection system; the clamping force is 100 T. The injection molding temperature is specifically: the first temperature section (barrel end) is 78-85°C, the second temperature section is 242-246°C, the third temperature section is 245-250°C, the fourth temperature section is 245-250°C, and the fifth temperature section (nozzle end) is 240-252°C.

[0012] The antistatic PBT contact lens mold can be manufactured by adopting the manufacturing method.

[0013] By adopting the above technical solution, the present invention achieves the following beneficial effects: 1. PP antistatic agent is compounded by fatty acid ester and fatty acid amide, which can provide long-term antistatic performance for plastic products, greatly reduce the surface resistance of products, and eliminate static electricity. In addition, PP antistatic agent has good thermal stability and suitable compatibility with resin. Adding it to PBT mold material can reduce the adhesion of impurities in PBT mold, prevent static electricity accumulation, make the demoulding process of lenses more convenient, and significantly improve the yield and stability of fully molded silicone hydrogel lenses.

[0014] 2. Modifiers ABS resin, PC and TPU are added to the PBT contact lens mold of the present invention, wherein ABS resin has good stability, small molding shrinkage and good low-temperature impact resistance, PC has excellent impact resistance, transparency, heat resistance and dimensional stability, TPU has high mechanical strength and outstanding cold resistance, still maintains good elasticity and flexibility at -35 degrees, and has excellent processability during PBT mold processing.

[0015] 3. The present invention adopts a new PBT contact lens mold formula to modify the PBT material, and obtains a PBT contact lens mold with good antistatic and mechanical properties by controlling roller refining and injection molding parameters. The PBT contact lens mold is used to produce contact lenses by full molding method, and the product yield can reach more than 96%. DETAILED DESCRIPTION

[0016] The method for making the antistatic PBT contact lens mold of the present invention is described in detail below through specific embodiments.

[0017] In the following embodiments of the present invention, the extruder is a Tengda twin-screw extruder (TSH-52P), the injection molding machine is a FANUC ROBOTSHOT precision electric injection molding machine (α-S100iB), the clamping force is 100 T, and it has a five-stage temperature-controlled melt injection system.

[0018] Example 1 This embodiment provides an antistatic PBT contact lens mold, which improves the lens yield by reducing the mold surface resistance.

[0019] In parts by weight, the formula of the antistatic PBT contact lens mold is: 70 parts of PBT resin, 5 parts of PP antistatic agent, 10 parts of ABS resin, 10 parts of PC, and 5 parts of TPU; the production method comprises the following steps: (1) Material preparation: Mix PBT resin, PP antistatic agent and modifier evenly according to the formula to obtain a mixed material for later use; (2) Extrusion granulation: The mixed material in step (1) is roll-milled on an extruder, the screw speed is 40 r / min, the first temperature section to the eighth temperature section are all 250°C, and the ninth temperature section is 255°C. The roll-milled modified PBT resin is hot-cut granulated on the extrusion head of the extruder to obtain a granular PBT modified material, which is then dried for later use; (3) PBT mold injection: Install the injection mold on the mold frame of the precision injection molding machine and start the precision injection molding machine; pour the granular PBT modified material dried in step (2) into the material barrel. The injection molding conditions are as follows: Injection temperature: 80°C in the first temperature section (barrel end), 245°C in the second temperature section, 250°C in the third temperature section, 250°C in the fourth temperature section, and 245°C in the fifth temperature section (nozzle end); holding speed is 18 mm / s, injection pressure is 680kgf / cm 2 , the injection time is 1.5s, the holding time is 3.5s, the cooling time is 15s, injection molding and injection are performed to obtain a PBT contact lens mold.

[0020] The mold was used to produce 1000 contact lenses, of which 9 were damaged due to difficulty in demolding, 11 had impurities during surface quality inspection, and 10 had broken edges, with a yield rate of 97.0% (Table 2).

[0021] Comparative Example 1 The other conditions or parameters of Comparative Example 1 are the same as those of Example 1, and only the mold formula is changed; in parts by weight, the mold formula is: 70 parts of PBT resin, 10 parts of ABS resin, 10 parts of PC, and 5 parts of TPU.

[0022] The obtained PBT contact lens mold was used to produce 1000 contact lenses, of which 142 were damaged due to difficulty in demolding, 48 had impurities during surface quality inspection, and 46 had broken edges. The yield rate was only 80.4% (Table 2).

[0023] Comparative Example 2 (Existing conventional formula) The other conditions or parameters of Comparative Example 2 are the same as those of Example 1, except for the mold formula; in parts by weight, the mold formula is: 90 parts of PBT resin, 3 parts of 2,6-di-tert-butyl-p-cresol (phenolic antioxidant), and 7 parts of pentaerythritol stearate (lubricant).

[0024] The obtained PBT contact lens mold was used to produce 1000 contact lenses, of which 159 were damaged due to difficulty in demolding, 48 had impurities during surface quality inspection, and 61 had broken edges, with a yield rate of only 70.2% (Table 2).

[0025] Example 2 This embodiment provides an antistatic PBT contact lens mold, which improves the lens yield by reducing the mold surface resistance.

[0026] In parts by weight, the formula of the antistatic PBT contact lens mold is: 75 parts of PBT resin, 5 parts of PP antistatic agent, 5 parts of ABS resin, 10 parts of PC, and 5 parts of TPU; the production method comprises the following steps: (1) Material preparation: Mix PBT resin, PP antistatic agent and modifier evenly according to the formula to obtain a mixed material for later use; (2) Extrusion granulation: The mixed material in step (1) is roll-milled on an extruder, the screw speed is 40 r / min, the first temperature section to the eighth temperature section are all 250°C, and the ninth temperature section is 255°C. The roll-milled modified PBT resin is hot-cut granulated on the extrusion head of the extruder to obtain a granular PBT modified material, which is then dried for later use; (3) PBT mold injection: Install the injection mold on the mold frame of the precision injection molding machine and start the precision injection molding machine; pour the granular PBT modified material dried in step (2) into the material barrel. The injection molding conditions are as follows: Injection temperature: 78°C in the first temperature section (barrel end), 242°C in the second temperature section, 245°C in the third temperature section, 248°C in the fourth temperature section, and 248°C in the fifth temperature section (nozzle end); holding speed is 20mm / s, injection pressure is 690kgf / cm 2 , the injection time is 1.9s, the holding time is 3.4s, the cooling time is 14s, and the PBT contact lens mold is obtained by injection molding and injection.

[0027] The mold was used to produce 1000 contact lenses, of which 12 were damaged due to difficulty in demolding, 10 had impurities during surface quality inspection, and 11 had broken edges, with a yield rate of 96.7% (Table 2).

[0028] Example 3 This embodiment provides an antistatic PBT contact lens mold, which improves the lens yield by reducing the mold surface resistance.

[0029] In parts by weight, the formula of the antistatic PBT contact lens mold is: 80 parts of PBT resin, 5 parts of PP antistatic agent, 5 parts of ABS resin, 5 parts of PC, and 5 parts of TPU; the production method comprises the following steps: (1) Material preparation: Mix PBT resin, PP antistatic agent and modifier evenly according to the formula to obtain a mixed material for later use; (2) Extrusion granulation: The mixed material in step (1) is roll-milled on an extruder, the screw speed is 40 r / min, the first temperature section to the eighth temperature section are all 250°C, and the ninth temperature section is 255°C. The roll-milled modified PBT resin is hot-cut granulated on the extrusion head of the extruder to obtain a granular PBT modified material, which is then dried for later use; (3) PBT mold injection: Install the injection mold on the mold frame of the precision injection molding machine and start the precision injection molding machine; pour the granular PBT modified material dried in step (2) into the material barrel. The injection molding conditions are as follows: Injection temperature: 82°C in the first temperature section (barrel end), 246°C in the second temperature section, 248°C in the third temperature section, 252°C in the fourth temperature section, and 250°C in the fifth temperature section (nozzle end); holding speed is 15mm / s, injection pressure is 650kgf / cm 2 , the injection time is 2.1s, the holding time is 3.5s, the cooling time is 13s, and the PBT contact lens mold is obtained by injection molding and injection.

[0030] The mold was used to produce 1000 contact lenses, of which 11 were damaged due to difficulty in demolding, 13 had impurities during surface quality inspection, and 11 had broken edges, with a yield rate of 96.5% (Table 2).

[0031] Example 4 This embodiment provides an antistatic PBT contact lens mold, which improves the lens yield by reducing the mold surface resistance.

[0032] In parts by weight, the formula of the antistatic PBT contact lens mold is: 85 parts of PBT resin, 5 parts of PP antistatic agent, 5 parts of ABS resin, 3 parts of PC, and 2 parts of TPU; the production method comprises the following steps: (1) Material preparation: Mix PBT resin, PP antistatic agent and modifier evenly according to the formula to obtain a mixed material for later use; (2) Extrusion granulation: The mixed material in step (1) is roll-milled on an extruder, the screw speed is 40 r / min, the first temperature section to the eighth temperature section are all 250°C, and the ninth temperature section is 255°C. The roll-milled modified PBT resin is hot-cut granulated on the extrusion head of the extruder to obtain a granular PBT modified material, which is then dried for later use; (3) PBT mold injection: Install the injection mold on the mold frame of the precision injection molding machine and start the precision injection molding machine; pour the granular PBT modified material dried in step (2) into the material barrel. The injection molding conditions are as follows: Injection temperature: 85°C in the first temperature section (barrel end), 245°C in the second temperature section, 248°C in the third temperature section, 250°C in the fourth temperature section, and 240°C in the fifth temperature section (nozzle end); holding speed is 16mm / s, injection pressure is 660kgf / cm 2 , the injection time is 1.2s, the holding time is 3.4s, the cooling time is 12s, and the PBT contact lens mold is obtained by injection molding and injection.

[0033] The mold was used to produce 1000 contact lenses, of which 11 were damaged due to difficulty in demolding, 9 had impurities during surface quality inspection, and 11 had broken edges, with a yield rate of 96.9% (Table 2).

[0034] Performance characterization test: The granular PBT modified materials obtained by step (2) of Examples 1-4 and Comparative Examples 1-2 were subjected to notched impact strength test, tensile strength test and elongation at break test, and the melt index and density of the materials were measured; wherein the notched impact strength test, tensile strength test and elongation at break test are shown below, and the notched impact strength, tensile strength, elongation at break, melt index and density of the materials are shown in Table 1.

[0035] (1) Notched impact strength test: Notched impact strength refers to the ratio of the energy absorbed by the notched specimen during the cantilever beam impact strength failure process to the original cross-sectional area of ​​the specimen.

[0036] (2) Tensile strength: Tensile strength is the maximum tensile stress that a specimen can withstand when an axial tensile load is applied to the specimen using a tensile testing machine under standard test conditions until the specimen breaks.

[0037] (3) Elongation at break: The elongation at break is the ratio of the increment of the working part gauge length to the initial value when the specimen is tensile fractured.

[0038] Table 1 Performance data of granular PBT modified materials prepared in Examples 1-4 From the notched impact strength, tensile strength and elongation at break data in Table 1, it can be seen that the granular PBT modified materials prepared in Examples 1-4 of the present invention all have good mechanical strength, and the melt index is greater than 60g / 10min, indicating that the material has good fluidity; the density is greater than 1.3 g / cm 3 The higher the density, the smaller the surface mold gap, which provides a good basic condition for the injection molding of the PBT mold in step (3).

[0039] The top thickness and base curve data of the PBT contact lens mold obtained by step (3) in Examples 1-4 were measured, and the surface state of the mold was observed with a 10× magnifying glass. The mold was used to produce 1000 contact lenses. The results are shown in Table 2.

[0040] Table 2 Performance data of PBT contact lens molds made in Examples 1-4 It can be seen from the data in Table 2 that the yield rate of the finished products of the molds made by adding PP antistatic agent (Example 1) and not adding PP antistatic agent (Comparative Example 1) for full-molding production of contact lenses differs by more than 16%, and the yield rate of the finished products of the molds made by the formula of the present invention and the molds made by the existing conventional formula for full-molding production of contact lenses is improved by more than 26%, and the yield rate improvement effect is significant.

Claims

1. A method for making an antistatic PBT contact lens mold, characterized in that: The formula of the antistatic PBT contact lens mold is as follows: 70-85 parts of PBT resin, 5 parts of PP antistatic agent, and 10-25 parts of modifier by weight; the preparation method comprises the following steps: (1) Material preparation: Mix PBT resin, PP antistatic agent and modifier evenly according to the formula to obtain a mixed material for later use; (2) Extrusion granulation: The mixed material in step (1) is roll-milled on an extruder at a rolling temperature of 250-255° C. The modified PBT resin after roll milling is hot-cut granulated on the extrusion head of the extruder to obtain a granular PBT modified material, which is then dried for later use; (3) PBT mold injection: Install the injection mold on the mold frame of the precision injection molding machine and start the precision injection molding machine; pour the granular PBT modified material dried in step (2) into the material barrel. The injection molding conditions are as follows: Injection temperature 78~252℃, holding speed ≤20mm / s, injection pressure ≤700 kgf / cm 2 , injection time ≤ 2s, holding time ≤ 4s, cooling time ≤ 15s, injection molding and injection, to obtain a PBT contact lens mold.

2. The method for making an antistatic PBT contact lens mold according to claim 1, wherein: The modifier is a mixture of acrylonitrile-butadiene-styrene terpolymer (ABS resin), polycarbonate (PC) and polyurethane elastomer (TPU).

3. A method for making an antistatic PBT contact lens mold as claimed in claim 2, characterized in that: The mixing mass ratio of the ABS resin, PC and TPU is 1-5:1-3:1-2.

4. The method for making an antistatic PBT contact lens mold according to claim 1, wherein: In step (2), the extruder is a twin-screw extruder.

5. The method for making an antistatic PBT contact lens mold according to claim 4, characterized in that: In step (2), the screw speed of the twin-screw extruder is 30-50 r / min.

6. The method for making an antistatic PBT contact lens mold according to claim 5, characterized in that: In step (2), the rolling temperatures in the first temperature section to the eighth temperature section are all 250°C, and the rolling temperature in the ninth temperature section is 255°C.

7. The method for making an antistatic PBT contact lens mold according to claim 6, characterized in that: In step (3), the precision injection molding machine has a five-stage temperature-controlled melt injection system.

8. The method for making an antistatic PBT contact lens mold according to claim 7, characterized in that: In step (3), the clamping force of the precision injection molding machine is 100 T.

9. The method for making an antistatic PBT contact lens mold according to claim 7, characterized in that: In step (3), the injection molding temperature is specifically as follows: the first temperature section is 78-85°C, the second temperature section is 242-246°C, the third temperature section is 245-250°C, the fourth temperature section is 245-250°C, and the fifth temperature section is 240-252°C.

10. An antistatic PBT contact lens mold made by the manufacturing method according to any one of claims 1 to 9.

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