JP4890344B2 - Lens array - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lens array which is excellent in material balance between heat resistance and mechanical strength, and is reduced in appearance defectives, especially, a sink mark. <P>SOLUTION: The lens array is made of methacrylic resin. The methacrylic resin is composed of 85 to 98.5 wt.% of methyl methacrylate monomer unit and 1.5 to 15 wt.% of at least one kind of other vinyl monomer unit copolymerizable with the methyl methacrylate. The weight-average molecular weight measured by Gel Permeation Chromatography (GPC) is 60,000 to 230,000, and the methacrylic resin contains 7 to 25% of the weight-average molecular weight component equal to or less than 1/5 of a peak weight-average molecular weight (Mp) in a GPC elusion curve. <P>COPYRIGHT: (C)2009,JPO&amp;INPIT

Description

  The present invention relates to a lens array made of methacrylic resin.

  Methacrylic resin is characterized by having a higher light transmittance, weather resistance, and rigidity than other plastic transparent resins as a transparent resin, such as lighting fixtures, building materials, signboards, nameplates, paintings, windows for display devices, etc. Used in a wide range of applications.

  On the other hand, in recent years, applications that are very difficult to mold are increasing. For example, in the field of lighting / display devices, etc., there is a general tendency to increase in size and thickness, and the demand for large and thin molded products or uneven molded products as lens arrays is increasing. These lens arrays are, for example, those that are finally assembled and fixed in the unit, etc., because they have positioning with the outer frame and the degree of freedom of the shape, and further, secondary processing such as cutting and router processing can be omitted in the subsequent process. An increasing number of cases employ injection molding.

  However, up to now, large and thin molded products have had problems such as cracking when assembled into a unit, as well as being easy to crack when released from a molding die. When this problem was designed and improved with the conventional acrylic resin technology, the only way to increase the strength was to increase the molecular weight. However, when the molecular weight is increased, the fluidity is deteriorated and molding at a high temperature is required. For this reason, the thermal decomposability of the resin is deteriorated, and at the same time, the resin is taken out from the mold while the temperature inside the resin is still high. Therefore, shrinkage is increased and sink marks are generated. This sinking causes the lens shape to be different from the designed one, and in the fields of lighting and display devices, the light distribution changes, resulting in uneven brightness, which is a big problem.

  In addition, even in the case of a molded product with uneven thickness as shown in FIG. 1, the cracks in the thin part and the sink in the thick part are large in the balance of mechanical strength and fluidity of the conventional acrylic resin. It was not obtained.

  If a large amount of other vinyl monomers copolymerizable with methyl methacrylate is copolymerized in order to improve the fluidity, the heat resistance will be lowered even if the fluidity can be improved. In a high-luminance display device, the temperature near the light source is high, and there have been cases where deformation has been observed even with conventional acrylic resins. In recent years, in display devices using LEDs as light sources, the technology of heat dissipation has advanced and the temperature around the light source seems to be lower than before, but considering the risks such as changes in the environmental atmosphere, conventional acrylic resins It is necessary to avoid lowering the heat resistance level.

  Until now, as a known method for improving the mechanical strength and moldability of a methacrylic resin, a method of imparting fluidity with a low molecular weight methacrylic resin and imparting mechanical strength with a high molecular weight or a micro-crosslinked structure is known. Relatedly, techniques for melting and mixing high molecular weight or low molecular weight methacrylic resins or expanding the molecular weight distribution using a branched structure have been reported (for example, see Patent Documents 1, 2, 3, and 4).

  However, the methacrylic resin described in Patent Document 1 simply mixes two methacrylic resins having different molecular weights, and does not satisfy high fluidity and mechanical strength at the same time. Patent Document 2 describes a technique in which a methacrylic resin constituting a low molecular weight is copolymerized in a large amount with another vinyl monomer copolymerizable with methyl methacrylate. However, the fluidity of the resulting methacrylic resin is insufficient.

  In the method for producing a finely crosslinked methacrylic acid resin using the polyfunctional monomer described in Patent Document 3, there is a problem that it is very difficult to control the polyfunctional monomer. When the amount of the polyfunctional monomer is too large, the mixing uniformity is lowered and the appearance of the molded product is lowered. On the other hand, if the amount of the polyfunctional monomer is too small, there is no effect of improving fluidity and maintaining mechanical strength.

  The methacrylic resin described in Patent Document 4 is also a mixture of two methacrylic resins having different molecular weights, and has low heat resistance and does not satisfy the balance between high fluidity and mechanical strength at the same time.

Japanese Patent Publication No. 1-2865 JP-A-4-277545 Japanese Patent Laid-Open No. 9-207196 JP 2006-328389 A

  An object of the present invention is to provide a lens array that has an excellent balance of physical properties of heat resistance and mechanical strength, and has reduced appearance defects, particularly sink marks.

  As a result of intensive studies to solve these problems, the present inventors have achieved a balance between physical properties of heat resistance and mechanical strength by using a methacrylic resin having a specific low molecular weight component in a specific ratio range. The inventors have found that a lens array with reduced appearance defects, in particular sink marks, can be obtained while maintaining the present invention, thereby completing the present invention.

That is, the lens array of the present invention is
A lens array made of methacrylic resin,
The methacrylic resin is
Consists of 85 to 98.5 wt% of methyl methacrylate monomer units and 1.5 to 15 wt% of at least one other vinyl monomer unit copolymerizable with methyl methacrylate,
The weight average molecular weight measured by gel permeation chromatography (GPC) is 60,000-230,000,
It is characterized by containing 7 to 25% of a weight average molecular weight component of 1/5 or less of the peak weight average molecular weight (Mp) in the GPC elution curve.

  ADVANTAGE OF THE INVENTION According to this invention, while being excellent in the physical property balance of heat resistance and mechanical strength, the lens array with which the appearance defect (sink) was reduced can be provided.

  Hereinafter, the present invention will be described in detail.

  The lens array referred to in the present invention is a lens in which a plurality of single lenses are arranged. For example, a lens having a continuous lens shape is repeated, and the single lenses are arranged in the X direction or in the XY direction as a surface. An integrated type is also included. There is no restriction | limiting in the shape of a single lens, For example, a general uneven | corrugated R lens shape, a prism shape, a pyramid shape, a saddle-shaped lens shape, a Fresnel lens shape, a moth eye lens shape, a lenticular lens, a fly eye lens etc. are mentioned. Further, the size of the lens is not limited, and includes a microlens to a gentle R shape.

  FIG. 1 shows a push button of a cellular phone as an example of the lens array of the present invention. In the lens array shown in FIG. 1, a plurality of single lenses 1 that are thick portions are arranged, and portions other than the single lenses 1 are connected by a thin portion, which is an integral molded product. Is also called a connecting lens. Mobile phone push buttons are built in a fixed location, and considering the efficiency of assembly, it is a great merit that all buttons are connected.

  In addition to those shown in FIG. 1, the single lenses 1 are regularly arranged in a plane in the XY direction, arranged in a straight line only in the X direction, arranged randomly in the design, and the shape of the single lens 1. Various shapes can be envisaged, such as those in which the thickness and size differ depending on each function, and any of the lens arrays of the present invention is included. In addition to mobile phone push buttons, display indicators are also included.

  Furthermore, in particular, as a lens for LED light sources that has spread rapidly in recent years, in order to efficiently pick up the light of the LED, a hole for putting the LED into the apex of the inverted triangular pyramid is formed so as to enclose one LED. In addition, a lens for an LED light source is also included in which a single lens is covered with each LED in which LEDs are spread in the XY directions as surface light sources at intervals of 10 mm, and this is formed into an integral molded product.

  The lens array of the present invention preferably has a thin portion of 1.5 mm or less, preferably 1.2 mm or less, more preferably 1.0 mm or less from the viewpoint of thinness and weight reduction, and is such an injection molded product. It is more preferable. Even a thin-walled product can be easily injection-molded by using a methacrylic resin, which will be described later, and the molded product is less distorted. In addition, at the time of injection molding, the thin-walled product cools quickly after being taken out from a mold or the like, and cracks due to cooling distortion are less likely to occur.

  The lens array of the present invention preferably has a thick portion of 3 mm or more, preferably 10 mm or more, more preferably 15 mm or more, and more preferably such an injection molded product. When the wall thickness is thick, the inside is still removed from the mold at a high temperature, so sink marks are a problem. However, since the methacrylic resin used in the present invention has high fluidity, the resin temperature and the mold temperature must be adjusted. It is possible to mold by lowering. Therefore, sink marks and distortion of molded products can be prevented.

  The lens array of the present invention has a complicated flow characteristic such as a connecting lens in which a thin part having a thickness of 1.5 mm or less and a thick part having a thickness of 3 mm or more are alternately repeated in a plane due to the excellent flow characteristics of the resin used. It is easy to injection mold even a molded product, and sink marks of the molded product can be reduced.

  In particular, it is suitable for a lens array composed of a single lens, such as a convex lens, a concave lens, a pickup lens, a projector lens, an uneven thickness lens, a prism, and a mirror lens, where sink marks are likely to cause problems depending on the product shape.

  The heat resistance of the lens array of the present invention is preferably 100 ° C. or higher, more preferably 103 ° C. or higher in terms of Vicat softening temperature.

  Examples of the method for producing the lens array of the present invention include injection molding, extrusion molding, blow molding, vacuum molding, pressure forming, and stretch molding. The injection molding is preferably performed at a molding temperature of 180 ° C. or higher and 210 ° C. or lower and a mold temperature of 90 ° C. or higher and 110 ° C. or lower.

  The methacrylic resin used in the present invention comprises methyl methacrylate and at least one other vinyl monomer copolymerizable with methyl methacrylate.

Other vinyl monomers copolymerizable with methyl methacrylate affect fluidity and heat resistance. Examples of other vinyl monomers copolymerizable with methyl methacrylate include the following.
Alkyl methacrylate having 2 to 18 carbon atoms in the alkyl group, alkyl acrylate having 1 to 18 carbon atoms in the alkyl group;
Α, β-unsaturated acids such as acrylic acid and methacrylic acid, unsaturated group-containing divalent carboxylic acids such as maleic acid, fumaric acid and itaconic acid, and alkyl esters thereof;
Aromatic vinyl compounds such as styrene, α-methylstyrene, styrene having a substituent on the benzene ring;
Vinyl cyanide compounds such as acrylonitrile and methacrylonitrile;
Maleic anhydride, maleimide, N-substituted maleimide and the like;
Ethylene glycol such as ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, tetraethylene glycol di (meth) acrylate, etc. Esterified;
What esterified the hydroxyl group of two alcohols, such as neopentylglycol di (meth) acrylate and di (meth) acrylate, with acrylic acid or methacrylic acid;
Esterification of polyhydric alcohol derivatives such as trimethylolpropane and pentaerythritol with acrylic acid or methacrylic acid;
Polyfunctional monomers such as divinylbenzene.

  These can be used alone or in combination of two or more. Among these, methyl acrylate, ethyl acrylate, n-propyl acrylate, n-butyl acrylate, sec-butyl acrylate, 2-ethylhexyl acrylate, and the like are preferable from the viewpoints of light resistance, heat resistance, and fluidity. Used. Methyl acrylate, ethyl acrylate, and n-butyl acrylate are particularly preferable, and methyl acrylate is most preferable because it is easily available.

  The content of methyl methacrylate units is 98.5 wt% or less from the viewpoint of the thermal decomposability of the resin. If it is this range, generation | occurrence | production of the bubble which a monomer called foaming produced | generated by decomposition | disassembly of the resin called silver at the time of shaping | molding will be suppressed. Moreover, it is 85 wt% or more from the point of heat resistance. If the heat resistance is high, distortion of the molded product can be suppressed during the environmental test. Preferably it is 90-98 wt%, More preferably, it is 92-97 wt%.

  The content of other vinyl monomer units copolymerizable with methyl methacrylate is 1.5 to 15 wt% with respect to the methacrylic resin. From the viewpoint of fluidity and heat resistance, it is 1.5 wt% or more, and from the viewpoint of heat resistance, it is necessary to be 15% or less. Preferably it is 2-10 wt%, More preferably, it is 3-8 wt%.

  The methacrylic resin used in the present invention has a weight average molecular weight measured by gel permeation chromatography (GPC) of 60,000 to 230,000. From the viewpoint of mechanical strength, it is 60,000 or more, and from the viewpoint of fluidity, it is 200,000 or less. In this range, the molding process is easy. Moreover, from a fluid viewpoint, Preferably it is 60,000-200,000, More preferably, it is 60,000-180,000, More preferably, it is 60,000-140,000.

  The weight average molecular weight is measured by gel permeation chromatography (GPC). Specifically, using a monodispersed standard methacrylic resin with a known weight average molecular weight and available as a reagent, and an analytical gel column that elutes a high molecular weight component first, a calibration curve is obtained from the elution time and the weight average molecular weight. Create it. The molecular weight of each sample can be obtained from the obtained calibration curve.

  The component having a weight average molecular weight of 1/5 or less of the peak weight average molecular weight (Mp) present in the methacrylic resin used in the present invention is important with respect to the mechanical strength of the resin and the appearance defect (sink) of the molded product. A component having a weight average molecular weight of 1/5 or less of Mp has a plasticizing effect. When the abundance of this component is in the range of 7 to 25% with respect to the methacrylic resin component, the effect of improving moldability and suppressing distortion of the molded product after molding can be obtained. It is 7% or more from the viewpoint of plasticizing effect and fluidity. If it is this range, the injection pressure at the time of shaping | molding can be suppressed, and distortion of the molded article by residual distortion can be prevented. On the other hand, it is 25% or less from the viewpoint of heat resistance, distortion of the molded product, and strength. Preferably, it is 8-23%, More preferably, it is 8-20%. In addition, the methacrylic resin component having a weight average molecular weight of 500 or less tends to cause a foam-like appearance defect called silver at the time of molding.

  Here, in the present invention, the peak weight average molecular weight (Mp) refers to the weight average molecular weight showing a peak in the GPC elution curve. When there are a plurality of peaks in the GPC elution curve, the peak is indicated by the weight-average molecular weight having the largest abundance. The content of the weight average molecular weight component of 1/5 or less of Mp can be determined as follows. That is, the area area (FIG. 2) in the GPC elution curve described below is divided by the elution time corresponding to 1/5 of the weight average molecular weight of Mp, and GPC elution corresponding to the weight average molecular weight component of 1/5 or less of Mp. Find the area of the area on the curve. From the ratio of the area and the area area in the GPC elution curve, the ratio of the weight average molecular weight of 1/5 or less of Mp can be determined.

  The other vinyl monomer copolymerizable with methyl methacrylate used in the present invention preferably has a higher composition ratio in the high molecular weight component of the resulting methacrylic resin than the composition ratio in the low molecular weight component. This is because heat resistance and appearance defects of molded products can be reduced, and fluidity can be further improved while maintaining mechanical strength.

  This point will be described with reference to FIGS. 2 to 4 are GPC elution curve measurement graphs, where the vertical axis is RI (differential refraction) detection intensity (mV), the horizontal axis is the elution time (min.) On the lower side, and the entire GPC area area is on the upper side. Indicates the cumulative area area (%). Moreover, in FIGS. 2-4, since the column eluted from a high molecular weight component is used, the high molecular weight component is observed at the beginning of the elution time, and the low molecular weight component is observed at the end of the elution time.

  In the present invention, the area of the hatched portion shown in FIG. 2 is referred to as “area area in GPC elution curve”. A specific method for determining the area of the area in the GPC elution curve is as follows. First, the point A at which the baseline 12 automatically drawn by the measuring instrument and the GPC elution curve 11 intersect the GPC elution curve 11 obtained from the elution time obtained by the GPC measurement and the detection intensity by the RI (differential refraction detector). And point B is determined. Point A is a point where the GPC elution curve 11 and the baseline 12 at the beginning of the elution time intersect. Point B is, as a rule, a position where the weight average molecular weight is 500 or more and the baseline 12 and the GPC elution curve 11 intersect. If the weight average molecular weight does not intersect within the range of 500 or more, the value of RI detection intensity at the elution time when the weight average molecular weight is 500 is defined as point B. A hatched portion surrounded by the GPC elution curve between the points A and B and the line segment AB is an area in the GPC elution curve. This area is the “area area in the GPC elution curve”.

  The “cumulative area area (%)” of the area area in the GPC elution curve is the high molecular weight side, that is, the point A shown in FIG. 2 is 0% which is the standard of the cumulative area area (%), and the low molecular weight side, that is, the elution time. From this point of view, the detection intensity corresponding to each elution time is accumulated, and the area area in the GPC elution curve is formed. A specific example of the accumulated area area is shown in FIG. In FIG. 3, a point on the baseline at a certain elution time is a point X, and a point on the GPC elution curve is a point Y. The ratio of the area surrounded by the curve AX, the line segment AB, and the line segment XY to the area area in the GPC elution curve is defined as the value of “cumulative area area (%)” at a certain elution time.

  Let Mh (wt%) be the average composition ratio of other vinyl monomer units copolymerizable with methyl methacrylate in the weight average molecular weight component (high molecular weight component) in the cumulative area of 0 to 2%. On the other hand, the average composition ratio of other vinyl monomer units copolymerizable with methyl methacrylate in the weight average molecular weight component (low molecular weight component) in the cumulative area of 98 to 100% is defined as Ml (wt%). FIG. 4 shows a schematic diagram of positions on the measurement graph of the accumulated area area of 0 to 2% and 98 to 100%.

  The values of Mh and Ml can be obtained by fractionating several times or several tens of times according to the column size based on the elution time obtained from GPC. The composition of the collected sample may be analyzed by a known pyrolysis gas chromatography method.

It is preferable that the relationship of the following formula (1) is established between Mh (wt%) and Ml (wt%) in the present invention.
(Mh-4.1) ≧ Ml ≧ 0 (1)

  This is because the average composition of other vinyl monomer units copolymerizable with methyl methacrylate is more than 4.1 (wt%) in the high molecular weight component than in the low molecular weight component, It shows that the vinyl monomer is not necessarily copolymerized. The difference between Mh (wt%) and Ml (wt%) is preferably 4.1 (wt%) or more, and more preferably 4.2 (wt%) or more for the effect of improving fluidity.

  Further, Ml is more preferably less than 0.5 (wt%), and further preferably less than 0.3 (wt%).

  That is, the average composition of other vinyl monomer units copolymerizable with methyl methacrylate of the methacrylic resin in the high molecular weight component is 4.1 (wt%) or more higher than the average composition of the low molecular weight component, and Ml is 0. It is preferable that the amount be less than 0.5 wt% because the heat resistance and the appearance defect of the molded product are reduced, and a dramatic fluidity improving effect is obtained while maintaining the mechanical strength.

  The methacrylic resin used in the present invention can be produced using the copolymer (1) and copolymer (2) shown below.

  The copolymer (1) is composed of at least one monomer selected from 99.9 to 100 wt% of a methyl methacrylate monomer and another vinyl monomer copolymerizable with methyl methacrylate. It is preferable that the amount of other vinyl monomers copolymerized with less than 1 wt% and copolymerizable with methyl methacrylate is small and may not be used. The molecular weight is preferably 5,000 to 30,000 in terms of weight average weight measured by gel permeation chromatography. Since the number of components having a weight average molecular weight of 500 or less causing problems in molding is reduced, the weight average molecular weight of the copolymer (1) is preferably 5,000 or more. In this case, when the copolymer (2) is produced in the presence of the copolymer (1), the molecular weight of the copolymer (2) is preferably stabilized during continuous production. 30,000 or less is preferable from the viewpoint of fluidity. More preferably, it is 5,000-25,000, More preferably, it is 6,000-20,000. The optimum range is 60,00 to 150,000.

  Copolymer (2) is a monomer composed of 80 to 99.5 wt% of methyl methacrylate monomer and 0.5 to 20 wt% of monomer composed of at least one other vinyl monomer copolymerizable with methyl methacrylate. The weight average molecular weight measured by gel permeation chromatography is preferably 70,000 to 230,000. 70,000 or more is preferable from the viewpoint of mechanical strength, and 230,000 or less is preferable from the viewpoint of fluidity. More preferably, it is 70,000-200,000, More preferably, it is 75,000-180,000.

  The ratio of the copolymer (1) is preferably 5 to 20 wt%. In order to obtain the effect of improving fluidity, 5 wt% or more is preferable, and 20 wt% or less is preferable from the viewpoint of the mechanical strength of the resin. More preferably, it is 5-17 wt%, More preferably, it is 5-15 wt%.

  The ratio of the copolymer (2) is preferably 95 to 80 wt%. In order to obtain the effect of improving fluidity, it is preferably 95 wt% or less, and preferably 80 wt% or more from the viewpoint of the mechanical strength of the resin.

  There is no restriction | limiting in particular as a manufacturing method of the composition of the methacryl resin used for this invention, Specifically, the following method is mentioned.

  1. The polymer (A) is produced in advance, and the polymer (A) is mixed with the raw material composition mixture of the polymer (B) having a molecular weight different from that of the polymer (A). A method of producing the mixture by polymerizing the mixture.

  2. After the polymer (A) is produced in advance, a raw material composition mixture of the polymer (B) having a molecular weight different from that of the polymer (A) is sequentially added to the polymer (A), or the polymer (A) is overlapped. A method of producing by sequentially adding to the raw material composition mixture of the combined body (B) and polymerizing.

  3. A method in which a polymer (B) having a molecular weight different from that of the polymer (A) and the polymer (A) is separately produced in advance and blended.

  These methods relate to the case where the two types of molecular weight components are different. However, with respect to methods 1 and 2, polymers (C) and polymers (D) having different molecular weight compositions can be produced in the same procedure. Good. Further, with respect to method 3, polymers (C) and polymers (D) having different molecular weight compositions may be further blended and melt kneaded with an extruder.

  Preferably, the polymer (A) is produced, and the polymer (B) is produced in a state where the polymer (A) is present in the raw material composition mixture of the polymer (B). This is because the compositions of the polymer (A) and the polymer (B) can be easily controlled, the temperature rise due to polymerization heat generation during polymerization can be suppressed, and the viscosity in the system can be stably obtained. In this case, the raw material composition mixture of the polymer (B) may be in a state where the polymerization is partially started. As a polymerization method for that purpose, bulk polymerization, solution polymerization, suspension polymerization or emulsion polymerization is preferred. More preferred are bulk polymerization, solution polymerization and suspension polymerization.

  Either the polymer (A) or the polymer (B) may have a high molecular weight, and either one may have a low molecular weight. The compositions of the polymer (A) and the polymer (B) are preferably different.

  For example, if the content of other vinyl monomers copolymerizable with methyl methacrylate is 1 to 20 wt% with respect to the methacrylic resin, the content differs between the polymer (A) and the polymer (B). It is preferable.

  Preferably, the polymer (A) is a copolymer (1) having a low molecular weight, the polymer (B) is a copolymer (2) having a high molecular weight, and more preferably the polymerization method is a copolymer. After producing (1), the copolymer (2) is produced in the presence of the copolymer (1).

The copolymer (1) used in the present invention can be copolymerized with the composition ratio Mal (wt%) of other vinyl monomer units copolymerizable with methyl methacrylate and the copolymer (2) with methyl methacrylate. It is preferable that the relationship of the formula (2) is established in the composition ratio Mah (wt%) of other vinyl monomer units.
(Mah-4.1) ≧ Mal ≧ 0 (2)

  The composition ratios Mal and Mah can be determined by measuring each of the copolymer (1) and the copolymer (2) by a pyrolysis gas chromatography method. Each value is almost the same as the composition ratio used in the preparation.

  The difference between Mah (wt%) and Mal (wt%) is preferably 4.1 (wt%) or more from the viewpoint of fluidity. When the high molecular weight copolymer (1) contains more vinyl monomer copolymerizable with methyl methacrylate as a composition ratio, fluidity is improved while maintaining heat resistance and mechanical strength. It is preferable because it can be achieved.

  That is, maintaining the difference between Mah (wt%) and Mal (wt%) to 4.1 (wt%) or more reduces the heat resistance and the appearance defect of the molded product, while maintaining the mechanical strength. It is preferable for improving fluidity.

  As a polymerization initiator for producing the highly fluid methacrylic resin of the present invention, the following general radical polymerization initiator can be used when free radical polymerization is used.

Di-t-butyl peroxide, lauroyl peroxide, dilauroyl peroxide, t-butylperoxy 2-ethylhexanoate, 1,1-bis (t-butylperoxy) -3,3,5-trimethylcyclohexane Peroxide systems such as 1,1-bis (t-butylperoxy) cyclohexane;
Azo series such as azobisisobutyronitrile, azobisisovaleronitrile, 1,1-azobis (1-cyclohexanecarbonitrile);

  These may be used alone or in combination of two or more. A combination of these radical initiators and an appropriate reducing agent may be used as a redox initiator. These initiators are generally used in the range of 0.001 to 1 wt% with respect to the monomer mixture.

  As a method for producing a methacrylic resin used in the present invention, a chain transfer agent generally used for adjusting the molecular weight of the polymer (A) and the polymer (B) when producing by a radical polymerization method. Can be used. Examples of the chain transfer agent include n-butyl mercaptan, n-octyl mercaptan, n-dodecyl mercaptan, 2-ethylhexyl thioglycolate, ethylene glycol dithioglycolate, trimethylolpropane tris (thioglycolate), pentaerythritol tetrakis (thioglycolate). Etc.) are preferably used. Generally, it is used in the range of 0.001 to 1 wt% with respect to the monomer mixture. The chain transfer agent used for the polymer (A) and the polymer (B) may be the same or different. The amount of chain transfer agent of polymer (A) and polymer (B) is determined depending on the desired molecular weight.

In the methacrylic resin used in the present invention, the following additives may be used as necessary.
Heat stabilizers such as dyes, pigments, hindered phenols and phosphates;
UV absorbers such as benzotriazole, 2-hydroxybenzophenone, and salicylic acid phenyl ester;
Plasticizers such as phthalate ester, fatty acid ester, trimellitic ester, phosphate ester, polyester, etc .;
Mold release agents such as higher fatty acids, higher fatty acid esters, mono-, di- or triglycerides of higher fatty acids;
Higher fatty acid esters, polyolefin-based lubricants;
Antistatic agents such as polyether-based, polyetherester-based, polyetheresteramide-based, alkyl sulfonate, alkylbenzene sulfonate;
Phosphorus, phosphorus / chlorine, phosphorus / bromine flame retardants;
Acrylic rubber obtained by multistage polymerization as a reinforcing agent;
Organic and organic inorganic light diffusing agents such as methyl methacrylate / styrene polymer beads and organic siloxane beads;
Inorganic light diffusing agents such as barium sulfate, titanium oxide, calcium carbonate, talc;

  Note that the light diffusing agent is effective in preventing glare of reflected light.

  There are no particular limitations on the method of blending these additives. For example, the additive is dissolved in the monomer mixture in advance and polymerized, or the resulting methacrylic resin is uniformly blended using a blender, tumbler, etc., and then added by compounding with an extruder. It is done.

  The methacrylic resin used in the present invention may be used alone or mixed with other resins. When mixing with other resins, they may be blended and mixed by heating and melting, or a plurality of pellets extruded by heating and melting and mixing may be blended and then mixed by heating and melting. The additives mentioned above may be blended and mixed at this time.

  The methacrylic resin used in the present invention may be a combination of a plurality of methacrylic resin compositions having different compositions, or may be combined with an existing methacrylic resin. As a combination method, they may be used by blending, or each resin may be once heated and melted, extruded, blended again, and pelletized.

  Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples.

[material]
The raw materials used are as follows.

Methyl methacrylate (MMA): manufactured by Asahi Kasei Chemicals (2.5 ppm of 2,4-di-6-tert-butylphenol) is added as a polymerization inhibitor. What)
Methyl acrylate (MA): manufactured by Mitsubishi Chemical (14 ppm of 4-methoxyphenol manufactured by Kawaguchi Chemical Industry as a polymerization inhibitor)
n-octylmercaptan: Arkema 2-ethylhexyl thioglycolate: Arkema Tricalcium phosphate: manufactured by Nippon Kagaku Kogyo Co., Ltd., used as a suspending agent Calcium carbonate: manufactured by Shiraishi Kogyo Co., Ltd., used as a suspending agent, sodium lauryl sulfate: manufactured by Wako Pure Chemicals, Suspension Used as auxiliary agent

[Measurement method]
[I. Measurement of resin composition and molecular weight]
1. Composition analysis of methacrylic resin The composition analysis of methacrylic resin was performed by pyrolysis gas chromatography and mass spectrometry.

Pyrolysis device: PY-2020D made by FRONTIER LAB
Column: DB-1 (length 30 m, inner diameter 0.25 mm, liquid phase thickness 0.25 μm)
Column temperature program: Hold at 40 ° C. for 5 min, then increase the temperature to 320 ° C. at a rate of 50 ° C./min, hold 320 ° C. for 4.4 minutes Pyrolysis furnace temperature: 550 ° C.
Column inlet temperature: 320 ° C
Gas chromatography: Agilent GC6890
Carrier: pure nitrogen, flow rate 1.0 ml / min
Injection method: Split method (split ratio 1/200)
Detector: JEOL mass spectrometer Automass Sun
Detection method: electron impact ionization method (ion source temperature: 240 ° C., interface temperature: 320 ° C.)
Sample: 10 μl of 10 g chloroform solution of 0.1 g methacrylic resin

  A sample was collected in a platinum sample cup for a thermal decomposition apparatus, vacuum-dried at 150 ° C. for 2 hours, and then the sample cup was placed in a thermal decomposition furnace, and composition analysis of the sample was performed under the above conditions. The composition ratio of the methacrylic resin was determined based on the peak area on total ion chromatography (TIC) of methyl methacrylate and methyl acrylate and the calibration curve of the following standard sample.

<Creation of standard sample for calibration curve>
The ratio of methyl methacrylate and methyl acrylate is (methyl methacrylate / methyl acrylate) = (100% / 0%), (98% / 2%), (94% / 6%), (90% / 10% ) (80% / 20%) were added to 50 g of each of the five solutions in total, 0.25% lauroyl peroxide and 0.25% n-octyl mercaptan. Each of these mixed solutions was put into a 100 cc glass ampule bottle, and the air was replaced with nitrogen and sealed. The glass ampoule bottle was placed in an 80 ° C. water bath for 3 hours and then in an oven at 150 ° C. for 2 hours. After cooling to room temperature, the glass was crushed and the methacrylic resin inside was taken out and subjected to composition analysis. A graph of (methyl acrylate area value) / (methyl methacrylate area value + methyl acrylate area value) and methyl acrylate charge ratio obtained by measurement of a standard sample for a calibration curve is used as a calibration curve. It was.

2. Measurement of weight-average molecular weight of methacrylic resin Measuring device: Gel analysis chromatography (LC-908) manufactured by Nippon Analytical Industry
Column: one JAIGEL-4H and two JAIGEL-2H, connected in series
In this column, the high molecular weight elutes early and the low molecular weight elutes slowly.
Detector: RI (differential refraction) detector Detection sensitivity: 2.4 μV / sec
Sample: 0.450 g of methacrylic resin in chloroform 15 ml Injection amount: 3 ml
Developing solvent: chloroform, flow rate 3.3 ml / min

  Under the above conditions, the RI detection intensity with respect to the elution time of the methacrylic resin was measured. The average molecular weight of the methacrylic resin was determined based on the area area in the GPC elution curve and the calibration curve.

  The following 10 methacrylic resins (manufactured by EasiCal PM-1 Polymer Laboratories) having different molecular weights and known monodispersed weight average molecular weights were used as standard samples for calibration curves.

Weight average molecular weight Standard sample 1 1,900,000
Standard sample 2 790,000
Standard sample 3 281,700
Standard sample 4 144,000
Standard sample 5 59,800
Standard sample 6 28,900
Standard sample 7 13,300
Standard sample 8 5,720
Standard sample 9 1,936
Standard sample 10 1,020

  When the polymer (1) and the polymer (2) are mixed, the GPC elution curve of the polymer (1) alone is measured in advance to determine the weight average molecular weight, and the polymer (1) is present. GPC in which the polymer (1) and the polymer (2) are mixed with each other by multiplying the GPC elution curve of the polymer (1) by the ratio (the charge ratio used in this example). By subtracting from the elution curve, a GPC elution curve of the polymer (2) alone is obtained. From this, the weight average molecular weight of the polymer (2) was determined.

  Moreover, the peak weight average molecular weight (Mp) in the GPC elution curve was calculated | required from the GPC elution curve and a calibration curve, and content of the weight average molecular weight component of 1/5 or less of Mp was calculated | required as follows.

  First, the area area (shaded area in FIG. 2) in the GPC elution curve of methacrylic resin is obtained. Next, the area area in the GPC elution curve is divided by the elution time corresponding to the weight average molecular weight of 1/5 of Mp, and the area area in the GPC elution curve corresponding to the weight average molecular weight component of 1/5 or less of Mp is calculated. Ask. From the ratio of the area and the area area in the GPC elution curve, the ratio of the weight average molecular weight of 1/5 or less of Mp was determined.

3. Measurement of composition ratio of vinyl copolymer copolymerizable with methyl methacrylate in high molecular weight component and low molecular weight component of methacrylic resin Molecular weight component having cumulative area of 0-2% shown in FIG. A certain molecular weight component was fractionated from the column based on the corresponding elution time, and the composition analysis was performed. Measurement and fractionation of each component are as described in 1. above. The same apparatus and conditions were used.

  That is, the fractionation was performed twice, and 10 μl of the fractionated sample was added to the above 1. The sample was collected in a platinum sample cup for a pyrolysis apparatus of the pyrolysis gas chromatography analysis and mass spectrometry method used in the above, and dried in a vacuum dryer at 100 ° C. for 40 minutes. Above 1. The composition of the methacrylic resin corresponding to the accumulated area area fractionated under the same conditions as above was determined.

[II. Measurement of practical properties]
1. Heat resistance (measurement of VICAT softening temperature)
Molding machine: 30t press molding machine Test piece: 4mm thickness
Measurement conditions: Based on ISO 306 B50 The VICAT softening temperature of the methacrylic resin was determined under the above conditions. This was used as an index for heat resistance evaluation.

2. Molding fluidity evaluation (measurement of spiral length)
This is a test for determining the relative fluidity based on the distance of the resin flowing through a spiral cavity having a constant cross-sectional area.

Injection molding machine: Toshiba Machine IS-100EN
Mold for measurement: Mold with 2mm deep and 12.7mm wide grooves on the surface of the mold in an Archimedean spiral shape from the center of the surface Injection conditions Resin temperature: 250 ° C
Mold temperature: 55 ° C
Injection pressure: 98 MPa
Injection time: 20 sec

A methacrylic resin was injected into the center of the mold surface under the above conditions. After 40 seconds from the end of the injection, the spiral molded product was taken out, the length of the spiral portion was measured, and used as an index for fluidity evaluation as follows.
◎: Excellent fluidity during molding and sufficiently good state ○: Fluidity during molding is good △: Fluidity during molding is slightly inferior ×: Fluidity during molding is poor and undesirable

3. Mechanical strength evaluation (strength evaluation based on the presence or absence of cracks during mold release of thin molded products)
Injection molding machine: JSW 350t electric injection molding machine Molded article size: Flat plate with 240mm width, 135mm length, 0.8mm thickness Gate: Film gate with 240mm width, 0.8mm thickness Gate installation position: Center in the width direction of the molded article Partial injection conditions Barrel temperature: 275 ° C
Mold temperature: 75 ℃
Injection speed: 800 mm / sec, constant holding pressure and holding time: 200 MPa, 20 sec
Removal of molded product: 40 seconds after the start of injection

Under the above conditions, methacrylic resin was injection molded. The cracked state of the thin part at the time of mold release was confirmed and used as an index for evaluating the mechanical strength as follows.
◎: Good state with sufficient strength without cracking when mold is released ○: Good condition when molded product is not cracked when releasing mold △: Cracked product when mold is released There is a state ×: The molded product is often cracked when the mold is released

4). Mold sink amount Injection molding machine: IS-100EN injection molding machine manufactured by TOSHIBA MACHINE Molded product: Mold for evaluation of sink marks (40 × 100 × 20t)
Injection conditions Barrel temperature: 200 ° C
Mold temperature: 100 ° C
Injection speed: 30 mm / sec, constant holding pressure and holding time: 100 MPa, 20 sec
Removal of molded product: 300 seconds after the start of injection

Sink marks at the center of the molded product obtained under the above conditions were measured visually and with a surface roughness meter (manufactured by Tokyo Seimitsu, Surfcom 558A) in the vertical and horizontal directions, and the Rmax values were averaged. And evaluated.
◎: Good appearance with no visible marks on the molded product appearance ○: Good condition with small shrinkage visually on the molded product appearance △: Slightly large sink marks on the molded product appearance ×: Visually visible on the molded product appearance Sink marks are large and unfavorable

[Examples 1-7, Comparative Examples 1-3]
Into a 60 L reactor, the raw material of the polymer (1) was added in the blending amount shown in Table 1, stirred and mixed, and suspension polymerization was carried out at a reaction temperature of 80 ° C. for 150 minutes to obtain a polymer (1). . This polymer (1) was sampled and the weight average molecular weight was measured. The results are shown in Table 1.

  Thereafter, the temperature is maintained at 80 ° C. for 60 minutes, and then the raw material of the polymer (2) is charged into the reactor at the blending amount shown in Table 1, followed by suspension polymerization at 80 ° C. for 90 minutes, and subsequently at 92 ° C. The temperature was raised at a rate of 1 ° C./min and ripened for 60 minutes to substantially complete the polymerization reaction. Next, the mixture was cooled to 50 ° C. and 20 wt% sulfuric acid was added to dissolve the suspending agent, followed by washing, dehydrating and drying treatment to obtain a bead polymer. The weight average molecular weight of this bead polymer was measured, and the weight average molecular weight of the polymer (2) was determined from the ratio of the polymer (1) shown in Table 1. The results are shown in Table 1.

  The bead polymer thus obtained was extruded at 240 ° C. with a twin screw extruder and pelletized. The results of measuring the composition and molecular weight of this pellet are shown in Table 2. Table 3 shows the evaluation results of practical physical properties.

[Comparative Examples 4 and 5]
The raw material of the polymer (2) is charged into a 60 L reactor at the blending amount shown in Table 1, suspended and polymerized at a reaction temperature of 80 ° C. for 150 minutes, and heated to 92 ° C. at a rate of 1 ° C./min. The polymerization was substantially completed after aging for 60 minutes. Next, the mixture was cooled to 50 ° C. and 20 wt% sulfuric acid was added to dissolve the suspending agent, followed by washing, dehydrating and drying treatment to obtain a bead polymer.

  The evaluation results are shown in Tables 1 to 3.

  The lens array of the present invention is suitable for a lens array composed of a single lens, such as a convex lens, a concave lens, a pickup lens, a projector lens, an eccentric lens, a prism, or a mirror lens, which is prone to sink marks depending on the product shape.

It is a figure which shows an example of the lens array of this invention. It is explanatory drawing of the area of an area in a GPC elution curve. It is the figure which showed an example of the accumulation area area. It is the schematic which shows the position of 0-2% of accumulation area areas, and 98-100% of accumulation area areas.

Explanation of symbols

1 Single lens 11 GPC elution curve 12 Baseline

Claims (7)

A lens array made of methacrylic resin,
The methacrylic resin is
Consists of 85 to 98.5 wt% of methyl methacrylate monomer units and 1.5 to 15 wt% of at least one other vinyl monomer unit copolymerizable with methyl methacrylate,
The weight average molecular weight measured by gel permeation chromatography (GPC) is 60,000-230,000,
A lens array comprising 7 to 25% of a weight average molecular weight component of 1/5 or less of a peak weight average molecular weight (Mp) in a GPC elution curve. Average composition of other vinyl monomer units copolymerizable with methyl methacrylate in the weight average molecular weight component in the cumulative area area 0-2% from the high molecular weight side of the area area in the GPC elution curve of the methacrylic resin The ratio Mh (wt%) and the average composition ratio Ml (wt%) of other vinyl monomer units copolymerizable with methyl methacrylate in the weight average molecular weight component in the cumulative area area of 98 to 100% The lens array according to claim 1, wherein the relationship is represented by the formula (1).
(Mh-4.1) ≧ Ml ≧ 0 (1)   The lens array according to claim 2, wherein the Ml is less than 0.5 wt%.   The lens array according to any one of claims 1 to 3, wherein the weight average molecular weight is 60,000 to 140,000.   The lens array according to any one of claims 1 to 4, comprising 8 to 20% of a weight average molecular weight component that is 1/5 or less of the peak weight average molecular weight (Mp).   The lens array according to claim 1, wherein the lens array has a thin portion of 1.5 mm or less.   The lens array according to claim 1, wherein the lens array has a thick portion of 3 mm or more.

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