JPS58198510A - Transparent plastic and its production - Google Patents

Abstract

PURPOSE:To obtain a transparent plastic having a heightened conversion in the stage of prepolymerization and good cuttability and grindability and suited for optical instruments and devices, by using a multi-component monomer mixture of a linear polymer-forming monomer, a crosslinking polyfunctional monomer and an alpha-methylstyrene dimer. CONSTITUTION:A multi-component monomer mixture of at least one monomer which, when homopolymerized, forms a linear polymer, e.g., methyl methacrylate (72-78pts.wt.), and at least one crosslinking polyfunctional monomer [e.g., ethylene glycol dimethyacrylate (20pts.wt.)] is mixed with 2-10wt%, based on the reaction system, alpha-methylstyrene dimer (2-8pts.wt.) and, preferably benzoyl peroxide and the prepolymerization of the mixture is effected so as to allow its volume shrinkage to proceed. Then, the main polymerization is effected to produce a transparent plastic having a light transmittance in the visible region of above 70%. The figures in the above parentheses indicate a formulation example.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a transparent plastic and a method for producing the same, and an object of the present invention is to provide a transparent plastic for use in optical instruments with a high prepolymerization rate and good cutting and polishing properties, and a method for producing the same. .

Conventionally, optical glass materials have often been used in optical instruments. However, glass materials have the drawbacks of being inferior to transparent plastics in terms of weight, brittleness, and difficulty in processing, so research and development of plastics as optical materials has been required. Unfortunately, only a few types of optical plastics are currently in practical use, such as diethylene glycol bisallyl carbonate, which is used for eyeglass lenses, and polymethyl methacrylate, polystyrene, and polycarbonate. When evaluating its physical properties, it is difficult to say that it is a reliable material.

There are four methods for manufacturing optical devices, especially lenses: injection molding, grinding and polishing, compression molding, and casting.

Optical elements such as lenses and prisms obtained by injection molding or compression molding have low precision in optical properties of the molding resin raw materials that are used as materials, and injection molding tends to cause molecular orientation in molded products. Its secondary physical properties are poor, and its use as a main component of optical equipment is limited. Furthermore, except for the weather resistance of polymethyl methacrylate, all resins are unreliable due to poor solvent resistance, weather resistance, and machinability.

The manufacturing method using mold polishing is described in the literature (Shunji Uchio "Asphericalization of Plastic Lenses" Optical Technology Contact 171979 3
As shown on page 4), it is a highly reliable lens manufacturing method,
Material supply is limited.

The casting method is an excellent method for molding lenses, and currently, diethylene glycol bisallyl carbonate (CR-
39), but is not used for other plastics. The biggest reason for this is that the volumetric shrinkage of the raw material monomers during electrodeposition is so large that it is virtually impossible to obtain a finished product.

Table 1 shows the polymerization volume shrinkage of various monomers.

It is said that the main reason for volume contraction in polymerization reactions is that the intermolecular distance due to the Van der Waal 1m' force in the monomer units changes to the distance of covalent bonds in the polymer. In order to reduce the polymerization volumetric shrinkage rate, a small amount of prepolymer or crosslinkable polyfunctional monomer such as ethylene glycol dimethacrylate is added to CR-39 or methyl methacrylate, and this is cooled to about -50°C. A method was proposed to obtain a strain-free polymer by polymerizing gamma rays and electron beams from cobalt (cobalt-60) etc. (Kaetsu Isao, "Development of organic glass materials for optical use", Optical Technology Contact 17, 1979, p. 31). , this has not yet been put into practical use. In certain ring-opening polymerizations, there are reaction systems that expand in volume, but there is little prospect of obtaining optically valuable polymers. In addition, the casting method for CR-39 currently used as eyeglass lenses takes a long polymerization time of 18 to 24 hours, causes large volume shrinkage (14%), and has poor precision in optical properties such as refractive index. Since it is not very expensive, it is not used in optical equipment other than eyeglasses.

Furthermore, reasons why cast polymerization is not carried out include that the resulting polymer is not transparent, the weather resistance of the polymer is poor, the polymer cannot be machined, and the accuracy of refractive index and dispersion is low, even if the polymer has a high refractive index. This is because even if this is obtained, the refractive index of each lens is not constant and it cannot be used for lenses that require design in advance. In general, it is easy to imagine that a polymer obtained from a multicomponent monomer system by mixing several monomers with high refractive indexes will have an appropriate refractive index and dispersion.

However, in actual production, it is extremely difficult to put the above method into practical use due to the adverse effect of volume shrinkage accompanying polymerization evolution, and this is clearly demonstrated by the fact that there are only a few types of optical plastics. In addition, it is common to introduce a crosslinked structure into the polymer as a means to improve the heat resistance of the resin and also to improve the machinability and polishing processability. If the amount is increased, the volume shrinkage during the polymerization reaction becomes large and cracking and death are likely to occur. Therefore, the amount of polyfunctional monomer used within a range that does not cause any practical problems is usually a few parts by weight based on the reaction system. It has been difficult to produce highly cross-linked polymers.

As a result of various studies, the present inventor found that, although volume shrinkage is unavoidable due to the conversion of monomers into polymers, if cast polymerization is performed after preliminarily increasing the polymerization rate of monomers, the following advantages can be obtained. I learned that there is.

1) Volumetric shrinkage during cast polymerization can be extremely suppressed.

2) The accuracy of optical physics of polymers can be improved by two to one orders of magnitude compared to conventional methods.

In addition, methods for improving the weather resistance, solvent resistance, or machinability of the polymer include: 1) Using at least one crosslinkable polyfunctional monomer in the mixed polymer.

2) As the monomer that becomes the linear polymer, a homopolymer having excellent weather resistance is used.

I realized that I should do something like this.

However, in general, in crosslinking polymerization, the reaction progresses rapidly from a certain point, and the liquid monomer state gels all at once and loses fluidity. It is difficult to keep it stable. This is the same with monomers that form linear polymers such as methyl methacrylate; in the case of casting methyl methacrylate, the prepolymerization rate is only a few percent, 3 to 4%.

Therefore, in order to make the mixed monomer (syrup) that has undergone low prepolymerization into a solid material without foaming after casting, it is necessary to react slowly at low temperature over a long period of time. For this reason, the polymerization volumetric shrinkage becomes large, resulting in an economically large energy loss, and it is extremely difficult to obtain the desired material.

The present inventors have conducted various studies in order to safely increase the prepolymerization rate of the crosslinkable mixed monomer. As a result, we focused on the following facts.

Literature (P.J. Flow, co-translated by Koten Oka and Kyo Kanamaru, "Polymer Chemistry" Chapter 2; Maruzen, C0H0E, Bawn, co-translated by Hisao Sato and Yuya Yamashita, "Chemistry of Polymers", Chapters 1-3) .

According to Gihodo), in the cross-linked polymerization or reaction process of a polymer having a network structure, the product at the initial stage is soluble in a solvent and is therefore considered to be a linear polymer.

Furthermore, in the polymerization of linear polymers, chain transfer agents such as n-butylmercaptan and m-dodecylmercaptan are added in order to adjust the molecular weight and shorten the reaction time. However, the present inventor has discovered that even in cross-linking polymerization, if some kind of chain transfer agent is used in the initial reaction stage, the number of linear polymer molecules will increase considerably.
As a result, most of the monomers are converted into polymers, the prepolymerization rate is increased, and we have come to believe that the volumetric shrinkage can be largely completed at the syrup stage. As a result of experiments, it has been found that at least one of the monomers in the multicomponent mixture must be a monomer whose homopolymer is a linear polymer. The desired polymer must be a transparent polymer. Table 2 shows examples of motsumar from which linear polymers can be obtained.

Many of these monomers are addition polymerization type monomers having a vinyl group.

Further, as the other one of the multicomponent mixed monomers, a crosslinked polyfunctional monomer shown in Table 3 should be used.

The chain transfer agent must satisfy the following conditions.

1) The chain transfer agent itself is not colored.

Also, the polymer should not be colored by this effect.

2) The refractive index should be as high as possible.

3) It is slow acting and therefore used in relatively large amounts.

4) It should be easy and safe to handle.

As a chain transfer agent that satisfies these conditions, α-methylstyrene dimer (2,4-diphenyl-4-methyl-1
-topentene), refractive index nD = 1.536 (25°C) was found to be most suitable. -Methylstyrene 2 has the chemical formula, stabilizes molecular radicals, and lowers the average degree of polymerization. Although it varies depending on the monomer, the action of α-methylstyrene dimer is 1/3 to 1/3 compared to the action of mercaptans.
The effect is 1/4.

In the crosslinking reaction, it was thought that the crosslinking would start from the beginning of the reaction, but this is not the case.It seems that the crosslinking reaction is closely related to temperature and starts abruptly above a certain temperature. In contrast, the growth of solvent-soluble molecules appears to take place before the crosslinking reaction begins, although this depends, of course, on the activation energy of the initiator used. Therefore, if the conversion to solvent-soluble molecules is carried out too quickly, the crosslinking reaction will be delayed. Based on this idea, as shown in the examples later, α-methylstyrene dimer is
By adding 10% by weight, it was possible to increase the prepolymerization rate to a maximum of 30% at once.

In this case, the residual volume shrinkage of the syrup is only a few percent, which is considered to be a dramatic advance from the common sense of conventional crosslinking polymerization reactions. Even if the prepolymerization rate was set to 15 to 20%, the residual shrinkage of the syrup was almost within 7%, making it extremely easy to manufacture materials for lenses and lens prisms by casting.

Regarding the refractive index of the monomers that produce linear polymers listed in Table 2, most of them have a qD of 1.42 or less, with the exception of monomers incorporating styrene or iodine.

Therefore, in order to increase the refractive index of the polymer, it is advantageous to select a comonomer with as high ηD as possible.

From this point of view, since the refractive index of α-methylstyrene dimer is high (1,536), the refractive index of the polymer also tends to be high.

Furthermore, the inventor measured each component of the mixed monomer with high accuracy, and strictly controlled the temperature and time during prepolymerization, and also carried out curing (also called post-reaction), which is the last step of the polymerization reaction.
We have discovered that the optical properties of the polymer obtained by precisely controlling the conditions can be made extremely stable. In terms of refractive index, the four digits after the decimal point are approximately constant within the range of ±2.

Therefore, if the casting mold is made to have the desired lens curve in advance, a plastic lens that meets the requirements can be easily obtained. It was found that not only was manual processing such as polishing unnecessary, but it was also possible to mass-produce high-precision aspherical lenses as long as a mold was prepared.

Since the polymer obtained by the present invention usually has a large volumetric shrinkage during the polymerization reaction, the polyfunctional monomer, which is used in only a few parts by weight based on the reaction system, is
By increasing the prepolymerization rate through the action of MSD, even when a large amount of polyfunctional monomer is used, up to several tens of parts by weight, there is no problem of distortion or cracking due to volumetric shrinkage. Both are crosslinked polymers and do not dissolve in most organic solvents or in the monomers of their original compositions. This is thought to be because it has a highly 3D network structure.

Also, speaking of the machinability of these polymers, the first
In lathe processing, there is no stickiness at all over the entire range of rotational speeds from low speed (250 R/M) to high speed (4500 R/M). High-speed steel is sufficient for the blade, but boron nitride or tungsten carbide is even better. Cutting chips are neatly connected without breaking into pieces, proving good machinability.

Secondly, it is well suited for cutting with a chip saw or a band saw. That is, the cut surface is smooth with almost no noticeable serrations, and there is no phenomenon of thermal adhesion or chipping.

This is in contrast to acrylic resin and polystyrene, which are prone to adhesion and chipping, and polycarbonate, where adhesion is a problem. Third, the polymers obtained according to the present invention can be mirror polished using a very common glass lens polisher. Therefore, it is suitable for making high-precision spherical lenses, and can be used in the same way as diethylene glycol bisallyl carbonate as a lens material for eyeglasses.

As mentioned above, the desired polymer must be transparent, but it is also desirable that it be hard and have excellent weather resistance. Furthermore, it is desirable to use a polymer that does not cause optical birefringence.The present inventors believe that methyl methacrylate is the most excellent monomer for producing linear polymers. Among the seven monomers shown in Table 2, the weather resistance of polymers using styrene, vinyl chloride, and vinyl acetate is not so good. Also, methyl acrylate, ethyl acrylate,
Polymers made with vinyl acetate, etc., are difficult to become hard. However, the hardness of the polymer is determined not only by the monomer composition, but also by the selection of the reaction initiator, and this polymer can be obtained even after heat treatment. It never gets hard.

Furthermore, polymers using styrene or vinyl iodide monomers tend to generate birefringence. For these reasons, methyl methacrylate monomer can be said to be the most excellent optical resin raw material.

To summarize the features of the present invention, it is a transparent plastic that has a light transmittance of 70% or more in the visible region (380 mμ to 800 mμ wavelength) due to a multicomponent mixed monomer of a monomer that becomes a linear polymer when used alone and a crosslinkable polyfunctional monomer. 1) A new plastic with a crosslinkable polyfunctional monomer that has a refractive index that exceeds the refractive index of the polymer, which is a linear polymer when used alone. 2) Copolymerization of a crosslinkable polyfunctional monomer with a monomer that forms a linear polymer when used alone. 3) By adding a dimer of d-methylstyrene to the above mixed monomer and adjusting the molecular weight through a chain transfer reaction,
A novel plastic 11 in which the volumetric shrinkage in the conversion of monomers to polymers can be largely terminated at the prepolymerization stage will now be described as an embodiment of the present invention.

Example 1 A composition was prepared by adding 0.1 part of benzoyl peroxide to a mixture of 78 parts (by weight, same hereinafter) of methyl methacrylate, 20 parts of ethylene glycol dimethacrylate, and 2 parts of α-methylstyrene dimer. 80 while stirring slowly.
Raise the temperature to ℃ over 2 and a half hours. After cooling this syrup to 20C with cold water,
Degas for a minute.

This syrup was injected between two glass plates through a 10 mm thick vinyl chloride gas foot, and after polymerizing for 40 hours in a glass cell dryer at 55°C, the temperature was increased from 55°C to 115°C. Raise the temperature over 4 hours, then 1
Cure for 2 hours at 15°C. The obtained polymer has a refractive index nD=1.4988 and a dispersion D=55.1.
It was transparent, had almost no optical defects, and had good reversibility into molds. The surface material had a pencil hardness of 4H.

Example 2 A composition in which 0.1 part of benzoyl peroxide was added to a mixture of 76 parts of methyl methacrylate, 20 parts of ethylene glycol dimethacrylate, and 4 parts of σ-methylstyrene dimer was poured in the same manner as in Example 1. Shape polymerization was performed. The obtained polymer had good transparency as in Example 1, and had almost no optical design. The surface hardness was 4H on a pencil hardness scale.

Example 3 A composition prepared by adding 0.1 part of benzoyl peroxide to a mixture of 72 parts of methyl methacrylate, 20 parts of ethylene glycol dimethacrylate, and 8 parts of thorn-methylstyrene dimer was cast in the same manner as in Example 1. Polymerization was carried out. The obtained polymer had good transparency, no optical defects, and a surface hardness of 4H on a pencil hardness scale.

Furthermore, when the polymers obtained in the above three examples were heated at 120°C for 1 hour, the original polymers did not deform or soften, and the heat resistance was good, making them suitable for cutting and polishing. .

The drawing is a diagram showing the spectral transmittance and spectral reflectance of the composition shown in Example 1 according to the present invention.

As shown in the examples above, in the single polymer of the present invention, a multicomponent mixed monomer containing at least one type of monomer forming a linear polymer and at least one type of crosslinkable polyfunctional monomer, d -By adding methylstyrene dimer to the 2nd to 10th reaction region, the adverse effect of monomer volume shrinkage during polymerization is removed, and a transparent plastic with high precision refractive index and excellent dispersion, cutting workability, and polishability is created. is obtained.

[Brief explanation of the drawing]

The drawing is a diagram showing the spectral transmittance and spectral reflectance of the composition shown in the first example of the present invention. Ding Tsuzukiura City (voluntary) 11 October 1957 2811 Japan Patent Office Kazuo Sugi 1, display of lit items Showfu 57τ1 Patent No. 82285! - Title of the invention 2 Transparent plastic and its surface display method 3 Ladle 1j11
Old 4, agent's drawing 8 Amendment included (1) Ming #t111 3rd negative line 16, 4th line 10th line, 6th line 11th line, 1st line 1st line, -
J 8th Tribute #! 8.9th line, 1st season 9th line 5.8, 1st page 15th line 14th, 1st page 16th line 12th, 1st season 9th line 21st
jij @ 3. Line 11 [Correct ``Egata'' in 1st entry to ``Chogata.'' (2) The description "mold polishing" in the fourth negative line 6 of Specification 4F is corrected to "grinding polishing". (3) The description of "-methylstyrene" in the 3rd and 4th lines of the 14th member of Specification 4 is corrected to [α-methylstyrene]. (4) The chemical formula stated on page 14, line 5 of the specification is corrected as follows. (5) [α-MS of Ming #111F No. 17 Sada 1st row
The description "DJ" has been corrected to "α-methylstyrene dimer." (6) The gt entry in lines 1 to 8 of the 20th draft of the specification is amended as follows. ``Create from room temperature to 80U while stirring 2##f11
! Raise the temperature over lJ and a half. Add this syrup 2 times with cold water.
"Cool to below 0'C" (Power) In the 5th line of the 22nd shell of specification 41F, the description "J" for "reaction" is corrected to "reaction system". (8) The drawing is corrected by adding an attached sheet. 9. List of attached documents (1 copy of 11 amended drawings)

Claims (5)

[Claims] (1) In the case of a single polymer, a multicomponent mixed monomer containing at least one type of monomer that becomes a linear polymer and at least one type of crosslinkable polyfunctional monomer, d
- Visible region (380wk11-8
00-wavelength) with a light transmission chamber of 70% or less. (2) The mixed composition is methyl methacrylate 72-7
8 parts by weight of ethylene glycol dimethacrylate, 20 parts by weight of ethylene glycol dimethacrylate, and 2 to 8 parts by weight of α-methylstyrene dimer. (3) The mixed composition is methyl methacrylate 72-7
The transparent plastic according to claim 1, comprising a composition in which benzoyl peroxide is added to a mixture of 8 parts by weight of ethylene glycol dimethacrylate, 20 parts by weight of ethylene glycol dimethacrylate, and 2 to 81 parts by weight of styrene dimer. d-
By adding 2 to 10% by weight of methylstyrene dimer to the reaction system, the volume of the system is reduced in the prepolymerization stage, and then the main polymerization reaction is carried out in the visible region (380 mμ~
A transparent plastic manufacturing method for manufacturing transparent plastic having a light transmittance of 70% or more at a wavelength of 800 mμ. (5) The method for producing a transparent plastic according to claim 3, wherein the crosslinkable multifunctional monomer contains 10 to 30% by weight of ethylene glycol dimethacrylate.