DE102008034153B4 - Process for producing optical lenses - Google Patents

Abstract

A method of manufacturing an optical element by injecting plasticized plastic into a mold cavity, wherein the fabrication of the optical element comprises at least three consecutive injections, the following steps being carried out:
Injecting a first quantity of plastic part, whereby a basic body is produced,
Injecting a second quantity of plastic part, whereby the basic body is at least partially coated,
- Injection of a third plastic part amount, is coated by the second plastic part coated base body at least partially, wherein the largest occurring wall thickness (t2) on the base body (2) applied second plastic subset smaller than the largest occurring wall thickness (t1) of the base body (2 ), characterized in that
- The third plastic subset is injected into a spaced from the mold cavity for the second plastic part amount by the first plastic part mold cavity and / or
- In the production of the base body (2) a curved surface is produced and when coating the base body (2) and / or of the second plastic part amount at least partially coated base body (2) varying wall thicknesses are generated.

Description

• - Einspritzen einer ersten Kunststoffteilmenge, wodurch ein Grundkörper hergestellt wird,
• - Einspritzen einer zweiten Kunststoffteilmenge, wodurch der Grundkörper wenigstens teilweise beschichtet wird,
• - Einspritzen einer dritten Kunststoffteilmenge, durch der mit der zweiten Kunststoffteilmenge beschichtete Grundkörper zumindest teilweise beschichtet wird.

The present invention relates to a method for producing an optical element, in particular an optical lens, by injecting plasticized plastic into a mold cavity, wherein the production of the optical element comprises at least three successive injection processes, wherein the following steps are carried out:

• Injecting a first quantity of plastic part, whereby a basic body is produced,
• Injecting a second quantity of plastic part, whereby the basic body is at least partially coated,
• - Injection of a third plastic part amount, is coated by the coated with the second plastic subset of base body at least partially.

According to the prior art, it is known to replace precision lenses made of glass with lens bodies, which are produced in the course of an injection molding process. For reasons of cost, the optical lenses produced in this way are used, for example, as lenses or lenses of camera phones or digital cameras. From the DD 298 620 A5 is an injection molding of plastic moldings has become known, wherein in a first process step, a molding is made, which differs from the final part in that certain functional surfaces are set back in a parallel distance. In a second injection molding cycle, this molding is extrusion-coated with molding compound, so that ultimately the final shape of the molding results.

The EP 0 696 955 B1 describes a method for producing photochromic lenses by injection molding, wherein two or more injections are provided to form the lens body.

The EP 0 839 636 B1 also describes a method for manufacturing optical lenses by injection molding, wherein the lens body is produced in the course of three separate injection processes, so that forms a homogeneous lens.

The EP 0 884 155 B1 describes a method of making a multicolor lens system that is made by injecting plastic into the mold cavity multiple times.

Finally, in the JP 2001-191365 A describes the production of optical lenses by injection molding, wherein a first plastic subset is injected into a first mold cavity, a further plastic subset in a second mold cavity and a further plastic subset in a third mold cavity. Although this method already has significant advantages, it has nevertheless been found that the production time of the entire lens takes a relatively long time.

The DE 10 2007 011 338 A1 discloses a method and apparatus for producing thick-walled plastic optical components by a multi-stage injection molding process.

The WO 2008/150988 A1 discloses a method and apparatus for making thick-walled plastic components by an injection molding process.

The production of thick-walled optical lenses made of transparent plastics (PMMA, PC, COC, PS) by injection molding or injection compression molding today involves a number of challenges. In the field of light optics today contour deviations of 5 to 30 μm are tolerated, even less in the field of imaging optics. Shrinkage differences between thick-walled and thin-walled areas have a negative effect on the contour accuracy. A plano-convex lens thus tends to have a sink mark in the middle of its greatest wall thickness. According to the state of the art, this can be counteracted only with very long hold-up times during injection molding or long embossing times during injection-compression molding. The reprinting period is limited by the freezing of the sprue, during embossing by the formation of a solidified surface layer. In injection molding usually a very thick sprue is expedient, which has a higher material consumption.

The cooling time by injection molding increases with the square of the wall thickness. The typical wall thickness for injection molding can be given as around 2.5 mm. Optical lenses sometimes have wall thicknesses of 5 to 20 mm at the thickest points. Cycle times of several minutes are common.

The most important parameters influencing the contour accuracy of optical components have been found to be the holding time (or embossing time) and the remaining cooling time. High quality often means low profitability.

The object of the present invention is to provide an improved injection molding process for the production of - in particular thick-walled - optical lenses or other optical elements such. Specify prisms, etc., whereby the entire cycle time of the production of the optical element can be shortened.

This is inventively achieved in an advantageous embodiment in that the largest occurring wall thickness of the second plastic part quantity applied to the base body is chosen smaller than the largest occurring wall thickness of the base body.

It is provided that not only a single surface coating is applied to a lens base produced in the course of an injection process to form a lens surface, but that the coating takes place in the course of several separate injection processes in several sub-layers, so that thus the shrinkage is relatively low.

The at least three successive injection events are not necessarily to be understood as immediately consecutive in terms of time. Rather, additional structure-changing process steps can be provided between the individual injection processes, such as an embossing process or the like. Also, during or after the inventive method in or on the lens surface diffractive structures are formed, for example in the manner of a Fresnel lens.

According to the present invention, it is proposed, in a first method step, to produce a lens base body by injecting plastic into the mold cavity, wherein the latter lingers longest in the tool and is also cooled for the longest. This fact can be exploited to optimize the cycle time. The wall thicknesses in the thick areas are to be chosen such that the first layer is the thickest and the subsequent layers are each thinner than the layer produced in the previous step. The first layer thus receives an optical surface, which must be produced in good quality already in the first step. The quality of the other side is less relevant, as sink marks can be compensated for overspray in the next station. The last layer receives another optical surface, this layer being thinnest. This arranged in the edge region of the optical lens edge zone thus suffers only a small shrinkage, which in turn has a positive effect on the contour accuracy. Thus, with the described method, both the contour fidelity of the surface is improved and the cycle time is minimized. Furthermore, the risk of free jet formation is significantly reduced since the lateral gating takes place in comparatively thin cavities. According to an advantageous development of the invention, it may also be expedient that the production of the optical lens also comprises more than three successive injection processes.

It can be advantageously provided that a method known from multicomponent technology is used (turntable, transfer, index plate, slide technology). Since an optical surface is formed in the first layer, it may be expedient to leave it in the same cavity during the further method steps in order to avoid damage. For this reason, a turntable method can be advantageously used.

In a preferred embodiment of the method according to the invention, it is envisaged that the injection process will be maintained at least between two of the at least three injection events until the respectively injected plastic has at least partially hardened.

In order to achieve favorable optical properties, it is advantageous if the largest occurring wall thickness of the second amount of plastic applied to the lens main body is smaller than the largest occurring wall thickness of the lens main body. In this context, it may also be favorable if the largest occurring wall thickness of the third plastic part quantity is smaller than the largest occurring wall thickness of the first plastic part quantity applied to the lens main body. In other words, an optical lens is produced which has a plurality of layers applied to the lens base body and in a plurality of separate injection processes.

Although the same plastic can always be used in the method according to the invention to produce a thick-walled lens body, different types of plastic can be injected instead. This means that a different type of plastic can be injected into the mold cavity at a later time than the first injected plastic. However, the plastic used should be chosen so that it is sufficiently transparent, depending on the intended use.

According to one exemplary embodiment of the invention, it can be provided that the mold cavity is arranged between a stationary and a movable mold part. In carrying out the method, it may be favorable if the mold cavity is substantially completely filled during each injection process. In this context, it may also be advantageous if the mold cavity is enlarged before or during each injection process.

Furthermore, it can be provided that in the course of an injection process at least one outer layer is injected and then the main body is injected.

• 1 eine durch das erfindungsgemäße Verfahren hergestellte plankonvexe Linse,
• 2 eine durch das erfindungsgemäße Verfahren hergestellte Linse mit ausgefüllten Außenflächen,
• 3 eine durch das erfindungsgemäße Verfahren hergestellte Linse mit Außenflächen, die in getrennten Schritten gespritzt werden.

Further details and advantages of the present invention will become apparent from the following description of the figures. Showing:

• 1 a plano-convex lens produced by the method according to the invention,
• 2 a lens produced by the method according to the invention with filled outer surfaces,
• 3 a lens produced by the method according to the invention with outer surfaces which are sprayed in separate steps.

1 shows schematically a plano-convex lens 1 made from at least three layers in the rotary table process. In a first method step, a lens base body is produced by injecting plastic into the mold cavity of the injection molding machine 2 made with the convex surface. The lens body 2 has a wall thickness t1, which is the largest occurring wall thickness of the individual layers. Due to the differences in wall thickness between center and edge, there will be more shrinkage in the middle, so you have to make sure that sinkholes appear on the side that will later be oversprayed. This can be achieved, for example, by choosing a lower mold temperature on the convex side in order to obtain a stable, frozen edge layer more quickly than on the opposite side. Shrinkage will therefore be more likely to affect that side with the weaker edge layer.

With a turntable is the lens body 2 turned to the second station and there with a layer 3a overmolded. The wall thickness t2 in the middle (along the optical axis A ) of this second layer 3a becomes smaller than the wall thickness t1 of the lens body 2 formed, wherein the total cooling time of the second layer 3a is lower and because of the lens body 2 acts as an insulator. The sink marks on the over-sprayed boundary layer are created by the newly injected material of the layer 3a compensated. Now, the rotation takes place in the third station, where sink marks from the second layer 3a be compensated and the formation of the planar lens surface (layer 3b ) he follows. The wall thickness t3 of the layer 3b is again lower than the wall thickness t2 of the second layer 3a ,

2 shows a further embodiment of a lens produced by the method according to the invention 1 , where first the two outer layers 3a and 3b the lens 1 be sprayed. In a further process step is between the outer surfaces 3a . 3b to form the lens body 2 Injected plastic and assembled into a molding. The thickness of the outer layers 3a . 3b is chosen so that they are sufficiently stable to not be deformed in the subsequent connection process.

3 shows a further embodiment of a biconvex lens 1 , In a first method step by injecting plastic into the mold cavity of the lens body 2 will be produced. In subsequent process steps, the two optical layers 3a . 3b injected in separate steps. In this context, it would also be possible in principle for a relatively inaccurate lens basic body to be used in a first method step 2 is produced, which is then converted into another cavity. After that, the lens body becomes 2 overmoulded on the surfaces.

All variants described could be carried out in one or more stations with injection compression molding instead of injection molding. The injection of the individual layers can preferably be done with separate injection units, the use of a single unit for all stations is also conceivable with special sprue structures. Of course, the optical surfaces 3a . 3b the lens 1 be further processed, in particular sanded or polished. In one embodiment variant, an embossing step can be provided between individual injection processes.

Claims (13)

A method of making an optical element by injecting plasticized plastic into a mold cavity, the manufacture of the optical element comprising at least three consecutive injections, comprising the steps of: injecting a first amount of plastic part to make a base, injecting a second amount of plastic part , whereby the base body is at least partially coated, - injecting a third plastic subset, is at least partially coated by the second plastic part coated base body, wherein the largest occurring wall thickness (t2) on the base body (2) applied second partial plastic amount smaller than the largest occurring wall thickness (t1) of the base body (2), characterized in that - the third plastic subset in one of the mold cavity for the second plastic part quantity by the first Kunststoffteilmeng e spaced mold cavity is injected and / or - in the production of the base body (2) has a curved surface is produced and at least partially during the coating of the base body (2) and / or with the second plastic part coated base body (2) varying wall thicknesses are generated. Method according to Claim 1 , characterized in that the optical element is an optical lens. Method according to Claim 1 or 2 , characterized in that the largest occurring wall thickness (t3) of the third plastic subset is smaller than the largest occurring wall thickness (t2) of the base body (2) applied first partial amount of plastic material. Method according to one of Claims 1 to 3 , characterized in that at least between two of the at least three injection events with the injection process is waited until the injected plastic is at least partially cured. Method according to one of Claims 1 to 4 , characterized in that the first, second and third plastic subset is formed from the same plastic. Method according to one of Claims 1 to 4 , characterized in that the first, second and third plastic subset is formed of a different plastic. Method according to one of Claims 1 to 6 , characterized in that a substantially transparent plastic is used for the first, second and third plastic part. Method according to one of Claims 1 to 7 , characterized in that the mold cavity is substantially completely filled during each injection process. Method according to one of Claims 1 to 8th , characterized in that the mold cavity is enlarged before or during each injection process. Method according to one of Claims 1 to 9 , characterized in that the shape and / or size of the mold cavity is changed in each injection operation by a rotary table method. Method according to one of Claims 1 to 10 , characterized in that at least one stamping operation is provided before a further injection process. Method according to one of Claims 1 to 11 , characterized in that in the course of an injection process, at least one outer layer (3a, 3b) is injected and then the base body (2) is injected. Method according to one of Claims 1 to 12 , characterized in that the second plastic subset and the third plastic subset are sprayed in separate steps.

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