JPH0618895B2 - Methacrylic resin molded products - Google Patents

Description

TECHNICAL FIELD The present invention relates to a methacrylic resin molded article, and more particularly to a heat-resistant methacrylic resin molded article having a small shape change and excellent gloss retention.

(Prior Art) Acrylic resins are used in various fields such as lighting covers, automobile parts, optical parts such as lenses due to their excellent weather resistance and outstanding transparency, but they are linear polymers. It has the drawback of insufficient heat resistance.

As one of the methods for improving this drawback, it is possible to partially cross-link and polymerize an alkyl methacrylate monomer or syrup into a gel polymer, and use this to produce a molded article (Japanese Patent Laid-Open No. 202128/1985). (Kaisho 62-2201)
Is proposed.

(Problems to be solved by the invention) According to this, a crosslinked resin molded product excellent in transparency and heat resistance can be obtained, but deformation and gloss during long-time use, especially in use under high temperature atmosphere It turned out to be a problem that loss often occurs.

According to the study by the present inventors, it has been found that the above problem is caused by a decrease in the degree of curing from the inside to the surface layer portion in the surface layer of the molded article.

(Means for Solving the Problem) As a result of further study, the present inventors have found that controlling the amount of residual double bonds in the vicinity of the surface is effective for solving the problem, and arrived at the present invention.

That is, the object of the present invention is to provide a crosslinked methacrylic resin molded article that does not cause deformation during use and change in surface appearance. A gel fraction of 15 is obtained by polymerizing 100 parts by weight of the unsaturated monomer (A) which may contain the coalescence together with 3 to 100 parts by weight of the crosslinking agent (B).
An article produced by re-polymerizing a partially cross-linked gel polymer obtained by terminating the polymerization at a point of ~ 75% under the conditions of giving a desired shape, the depth from the surface of the article. 0.3mm thick with the center of 0.9 to 1.0mm
The methacrylic resin molded article in which the average residual double bond of the monomer and the cross-linking agent is 4.5% or less, and the average residual double bond amount is substantially equal to or decreases from the depth to the surface. Reached by.

(Function) In the present invention, the unsaturated monomer (A) which is mainly composed of alkyl methacrylate and may contain a polymer thereof is an alkyl methacrylate alone or a main component of which is an alkyl methacrylate and is copolymerizable therewith. Α, β-
It is a syrup in which a mixture with an ethylenically unsaturated monomer or these polymers are dissolved and contained in the monomer or the monomer mixture. Alkyl methacrylate is methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, sec-butyl methacrylate, t.
Single or a mixture of ert-butyl methacrylate, lauryl methacrylate, cyclohexyl methacrylate, etc., but lower alkyl methacrylate, especially methyl methacrylate is preferred.

Examples of the copolymerizable monomer include alkyl acrylates such as methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate, cyclohexyl acrylate and lauryl acrylate, 2-hydroxyethyl acrylate, Hydroxyalkyl acrylates such as 2-hydroxypropyl acrylate and 3-hydroxybutyl acrylate, hydroxyalkyl methacrylates such as 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, 4-hydroxybutyl methacrylate and 2-hydroxy-3-chloropropyl methacrylate, Acrylic acid, methacrylic acid, neodymium acrylate, acrylate such as lead acrylate, methacryl Neodymium, methacrylate such as methacrylic acid lead, vinyl chloride, vinyl acetate, acrylonitrile, methacrolein nitrile, acrylamide, methacrylamide, styrene, α- methyl styrene, vinyl toluene, maleic anhydride.

The syrup containing the polymer of the alkyl methacrylate or the monomer mixture containing alkyl methacrylate as a main component generally has a viscosity of 1 to 20,000 centipoise at 25 ° C. and 3 to 40% by weight, preferably It is a monomer containing 6 to 20% by weight of a polymer.

A molding material composed of a partially crosslinked gel polymer obtained by polymerizing 100 parts by weight of the unsaturated monomer together with 3 to 100 parts by weight of a crosslinking agent and stopping the polymerization at a gel fraction of 15 to 75% is known. (JP-A-60-202128, 62)
-2201). Since the present invention uses such a partially cross-linked gel polymer, a detailed description of the cross-linking agent (B) used for the preparation thereof is not particularly required, but if it is roughly described, the cross-linking agent used in the present invention is: preferably has 10 or fewer atoms between the at least two (meth) acryloyl groups in the molecule (meth) acryloyl groups, for example, the following formula _{III~V MA-O- (CH 2)} n -O -MA (III) (Here, n is an integer of 3 to 6, and MA represents a methacryloyl group.) [Where R ₁ is H, CH ₃ , C ₂ H ₅ or CH ₂ O
H Represents H, CH ₃ , CH ₂ OCOC = CH ₂ (R ₄ represents H or CH ₃ ) or CH ₂ OH, R ₃ represents H or CH ₃ , and R ₁ , R ₂ and R ₃ represent At the same time, instead of hydrogen, (M) A represents a methacryloyl group or an acryloyl group. _{] (M) AC- (CH 2} CH 2 O) n - (M) A (V) ( wherein, n is 1 or 2, (M) A represents a methacryloyl group or an acryloyl group.) Represented by It is an unsaturated monomer.

Specifically, 1,3-propylene glycol dimethacrylate, 1,4-butylene glycol dimethacrylate, 1,6-hexanediol dimethacrylate, 1,
3-butylene glycol dimethacrylate, dimethylolethane dimethacrylate, 1,1-dimethylolpropane dimethacrylate, 2,2-dimethylolpropane dimethacrylate, trimethylolethane tri (meth)
Acrylate, trimethylolpropane tri (meth) acrylate, tetramethylolmethane tri (meth) acrylate, tetramethylolmethane dimethacrylate,
Examples thereof include ethylene glycol di (meth) acrylate and diethylene glycol di (meth) acrylate.

The amount of these cross-linking agents blended is the above-mentioned unsaturated monomer (A) 10
0 to 100 parts by weight, preferably 3 to 50 parts by weight
Parts by weight, most preferably 5 to 30 parts by weight.

In the present invention, a polymerization initiator is used when preparing the partially crosslinked gel polymer. This may be one or a mixture of two or more selected from ordinary low temperature active polymerization initiators and high temperature active polymerization initiators. Generally, a low temperature active polymerization initiator is suitable for the preparation of the partially crosslinked gel polymer.
Radical polymerization initiators of peroxides and azo compounds having a decomposition temperature of 50 ° C. or less, preferably 26 to 45 ° C., and particularly 26 to 41 ° C. for obtaining the time half-life are good. The amount thereof used is 0.002 to 1.0% by weight, preferably 0.0 to 1.0% by weight, based on the total amount of the unsaturated monomer (A) and the crosslinking agent (B).
It is from 05 to 0.1% by weight.

Examples of such a low temperature active polymerization initiator include (1)
Acetyl cyclohexyl sulfonyl peroxide, isobutyryl peroxide, cumylberoxy neodecanoate, diisopropyl peroxydicarbonate,
Dimyristyl peroxydicarbonate, 2,2'-azobis (4-methoxy-2,4-dimethylvaleronitrile), (II) di- (2-ethoxyethyl) peroxydicarbonate, di- (2-ethoxyethyl) ) Peroxydicarbonate, di- (2-ethylhexyl) peroxydicarbonate, (III) di- (3-methyl-3-methoxybutyl) peroxydicarbonate, t-butylperoxydecanoate, 2,2 ′ -Azobis (2,4
-Dimethylvaleronitrile), etc.
The compounds belonging to the groups (I) and (II) are preferred, and the compounds belonging to the group (I) are particularly preferred.

In the present invention, the high temperature active polymerization initiator is particularly suitable for polymerization under molding conditions, and a polymerization initiator having a decomposition temperature of 60 to 220 ° C. is preferably used in order to improve the molding cycle and maintain storage stability, and thus preferably 70 to A polymerization initiator having a decomposition temperature of 170 ° C. is preferable. The amount of the unsaturated monomer (A) used
And 0.02 to 5.0% by weight, preferably 0.05 to 4% by weight, based on the total amount of the crosslinking agent (B).

Examples of such a high temperature active polymerization initiator include (IV)
t-butyl cumyl peroxide, diisopropylbenzene hydroperoxide, di-t-butyl peroxide, p-menthane hydroperoxide, 1,
1,3,3-Tetramethylbutyl hydroperoxide, 2,5-dimethylhexane-2,5-dihydroperoxide, cumene hydroperoxide, t-butyl hydroperoxide, 1,1,2,2-tetra Phenyl-1,2-ethanediol, (V) 1,1-bis (t-butylperoxy) -3,3,5-trimethylcyclohexane, t-butylperoxylaurate, cyclohexanone peroxide, t-butylperoxide Oxyisopropyl carbonate, 2,2-bis (t-butylperoxy) octane, t-butylperoxyacetate, 2,2-bis (t-butylperoxy) butane, t
-Butylperoxybenzoate, di-t-butyldiperoxyisophthalate, methyl ethyl ketone peroxide, α, α'-bis (t-butylperoxyisopropyl) benzene, dicumyl peroxide, (VI) t
-Butyl hydroperoxide, m-toluoyl peroxide, benzoyl peroxide, t-butyl peroxyisobutyrate, octanoyl peroxide, lauroyl peroxide, succinic acid peroxide, acetyl peroxide, 1,1 '.
-Azobis (cyclohexane-1-carbonitrile) and the like, and among these, preferably (IV) and (V)
Compounds belonging to the group
It is a compound belonging to group V).

In the present invention, the partially crosslinked gel polymer is prepared by heating a mixture of the unsaturated monomer (A) and the crosslinking heavy agent (B) in the presence of a polymerization initiator to cause polymerization. This polymerization reaction is carried out at a temperature of 10 to 80 ° C, preferably 35 to 65 ° C for 10 to 200 minutes, preferably 20 to 150 minutes. Here, when both low-temperature active and high-temperature active polymerization initiators are used together, almost all of the low-temperature active polymerization initiator is consumed, but the high-temperature active polymerization initiator does not decompose at the reaction temperature and remains as it is. , Acts as a polymerization initiator under the subsequent molding conditions.

These high temperature active polymerization initiators may be added together with the low temperature active polymerization initiator at the time of preparing the partially crosslinked gel polymer, and may be added and mixed when kneading with a kneader or an extruder after preparation of the partially crosslinked gel polymer. Is also good.

The gel fraction of the partially crosslinked gel polymer is 15 to 75%, preferably 15 to 50%. The gel fraction here is
A partially crosslinked gel polymer was extracted in acetone added with a polymerization inhibitor with a Soxhlet extractor, and the sample weight dried after extraction was divided by the sample weight before extraction and expressed as a percentage.

If the gel fraction is less than 15%, it is necessary to keep the pressure in the mold for a long time in order to obtain a desired molded product, and foaming and cracks are likely to occur in the molded product. On the other hand, the gel fraction is 75%
If it exceeds, the fluidity is poor at the time of filling the cavity in the mold and the surface does not become smooth.

The partially cross-linked gel polymer having a desired polymerization rate can be obtained by stopping the polymerization reaction by quenching or the like. Furthermore, a mixture of the unsaturated polymer (A) and the cross-linking agent (B) is added to the polymerization initiator. It can be easily obtained by adding the following regulator in the heat polymerization in the presence of Such regulators include, for example, 1,4 (8) -P
-Menthadiene, 2,6-dimethyl-2,4,6-octatriene, 4,4-P-menthadiene, 1,4-cyclohexadiene and α-methylstyrene dimer.

Such regulators include the resin raw material (A) and the crosslinking agent (B).
And 0.0001 to 0.5% by weight, preferably 0.001 to 0.2% by weight, and most preferably 0.001 to 0.5% by weight.
It is used in the range of 005 to 0.1% by weight.

The methacrylic resin molded article according to the present invention is an article produced by polymerizing the above-mentioned partially crosslinked gel polymer again under the condition that a desired shape is imparted, and the depth from the surface of the article is 0. Thickness is 0.
The average residual double bond of 3 mm of the monomer and the cross-linking agent is 4.5.
% Or less, and the average residual double bond amount is substantially equal to or decreases from the depth toward the surface. A molded article which does not satisfy the above conditions, for example, a portion having a depth of 0.9 to 1.0 mm from the surface as the center, a thickness of 0.3 mm, and an average residual double bond amount of the monomer and the crosslinking agent of 4 When the average residual double bond amount in the surface layer portion is about 5% or less and about 6%, deformation or loss of gloss occurs after long-term use.

In the present invention, the amount of residual double bonds, by the infrared method,
It is determined from the absorption band peak height near 1620 nm, which is assigned to C = C. As a measuring method, a mixture of the unsaturated monomer and the cross-linking agent is diluted with a solvent which does not affect the absorption band peak, and a calibration curve of the concentration C = C is contained in advance, the measured thickness and the peak height. Then, the residual double bond amount is obtained from the calibration curve based on the peak height of the measurement portion of the molded product.

In the present invention, the wall thickness of the molded product is 2 to 20 mm, which is not strict and is defined in consideration of the wall thickness of the molded product which can be easily produced by using the partially crosslinked gel-like crosslinked polymer. It is something. The above-mentioned molded article is obtained by introducing the partially crosslinked gel polymer into a molding die mounted in a usual molding machine such as a compression molding machine, an injection molding machine, and a transfer molding machine, and polymerizing under the following conditions. It can be manufactured.

First, the molding die temperature is 70 to 120 ° C., preferably 80 to 120 ° C.
After raising the temperature to 110 ° C. to a desired constant temperature and filling the mold cavity with the gel polymer, an initial molding pressure of 20 to
Hold at 60 kg / cm ² for 15 to 120 seconds, and start raising the temperature within this time or after a lapse of time to reach 135 ℃ to 17 ℃.
A mold temperature of 0 ° C., preferably 145 ° C. to 160 ° C.,
And after the end of the initial molding holding pressure or after reaching a predetermined constant temperature, 1
The pressure is gradually increased to a molding pressure of 0 to 350 kg / cm ² and heat retention is performed for 1 to 5 minutes. After that, the temperature of the mold and the temperature at which the molded product is not deformed are cooled to 80 to 120 ° C., the mold is opened, and the molded product is taken out.

At this time, if the initial molding pressure is less than 20 kg / cm ² , the volume change due to polymerization shrinkage cannot be dealt with, and the molded product is cracked, foamed,
When a beard occurs and exceeds 60 kg / cm ² , the gel polymer flows out and the thickness of the molded article cannot be kept constant. On the other hand, when the reached temperature rise is less than 130 ° C. A molded article having a heavy bond amount cannot be obtained, and if the temperature exceeds 170 ° C., decomposition may occur, resulting in an increase in residual double bonds and yellowing of the molded product, which requires caution.

As a method of raising the mold temperature during the molding cycle, (1) a method of cutting a passage through which an oil is passed in a mold and passing a heat transfer oil heated to 170 ° C to 350 ° C into the passage, ( 2) A method of passing steam having a pressure of 25 to 30 kg / cm ² through a passage previously provided in the mold, (3) A coil is mounted in the mold with a material having good electric conductivity, and a high frequency current (5 KHz to 250 KHz) ) To the coil to heat the mold, which is a ferromagnetic material, and the cavity surface of the mold is heated.

Further, the partially crosslinked gel polymer used in the present invention has a shape-retaining property without stickiness, so that it can be handled in any shape such as a sheet, a rod, or a pellet, but a flake shape crushed by a crusher or a kneading machine. It may be kneaded in the form of a tablet without any problem, or an additive such as a colorant and a filler may be blended if necessary.

The methacrylic resin molded article thus obtained,
Unlike conventional constant temperature molded products, which have a large average residual double bond amount in the surface layer, 0.9 to 1.0 mm from the surface layer
It has a feature that the average residual double bond amount of thickness 0.3 mm is 4.5% or less around the entered part and the average residual double bond amount is equal to or decreases toward the surface layer part. Become.

(Examples) Hereinafter, the present invention will be described more specifically with reference to Examples.
The physical properties and performances of the synthetic resin molded articles obtained in Examples and Comparative Examples were measured by the following methods.

Gel Fraction The obtained partially crosslinked gel polymer was made into small pieces of 2 mm or less, and a sample whose weight (×) was measured in advance was extracted by a Soxhlet extractor in acetone containing 2% of hydroquinone at 50 ° C. for 10 hours, The sample weight after drying (y) was measured and calculated by the following formula to obtain the gel fraction (%).

Amount of residual double bond Paying attention to the peak height of absorption band due to absorbance near 1620 nm, which is assigned to C = C by infrared method, and the mixture of the unsaturated polymer and the crosslinking agent is a solvent which does not affect the absorption band peak. A calibration curve is prepared beforehand by diluting with C = C and the measured thickness and peak height, and the calibration curve is obtained from the peak height measured for the surface layer part cut from the molded product and the 0.3 mm plate thickness well inside. The amount of residual double bonds was determined from the above. A spectrophotometer (Model 323 manufactured by Hitachi, Ltd.) was used as a device for measuring the absorption peak.

The heat distortion temperature was tested based on ASTM D648.

Surface roughness measurement JIS with a surface roughness meter (AY-22 type, manufactured by Koita Seisakusho)
The surface roughness of the molded product was measured based on B0601, B1982. In addition, the mold was measured by polishing the same mold material by the same polishing method and made it correspond to the mold surface roughness.

Accelerated exposure Ultraviolet accelerated exposure tester (ALTAS- manufactured by Toyo Seiki Co., Ltd.)
UVcon) at 70 ° C for 4 hours at 50 ° C.
Only exposure to ultraviolet light at 0 ° C. was performed for a predetermined time in a cycle of 8 hours.

Taper wear A wear wheel CS-10F, a load of 500 g, and a rotation speed of 100 were used, and a wear test was performed based on ASTM D 1044.

Steel Wool Using a scratch tester manufactured by Toyo Seiki Seisakusho, pressure is 100 g / cm ² against scratch resistant film, traverse speed 16 mm / s
When using ec # 000 steel wool and moving 100 times, the ratio of diffuse transparency and total light transmittance is defined as the haze value according to JIS K 7105, and the difference between the haze value before and after the test is the scratch resistance of the steel wool. The test was conducted by setting it as sex.

Examples-1 to 4 80 parts by weight of methyl methacrylate syrup containing 8% by weight of polymethyl methacrylate having an average degree of polymerization of 23,000, 20 parts by weight of 2,2-dimethylpropanediol-1,3-dimethacrylate, 1,4 (8) -P-menthadiene 0.08 g / kg, 2,2'-azobis (4-methoxy-2,4-dimethyl) valeronitrile 0.03 g /
kg, di-t-butylperoxyhexahydrophthalate 0.5 g / kg, 2,2'-bis (t-butylperoxy) butane 1 g / kg and di-t-butylperoxide 3 g / kg were mixed and dissolved. 450 x mixture with 6 mm thickness
Two tempered glass plates with a width of 350 mm, using a gasket made of vinyl chloride resin, injected into the cells assembled so that the interval is 10 mm, and then placed in a constant temperature water tank preheated to 55 ° C. The cell was charged, polymerized for 2 hours and 30 minutes and then taken out to obtain a partially crosslinked gel polymer having a gel fraction of 35%. This partially cross-linked gel polymer, screw diameter 40φ,
A partially crosslinked gel polymer kneaded with a single-screw extruder with L / D = 15 was obtained.

On the other hand, a copper pipe with an outer diameter of 8φ and an inner diameter of 6φ was coiled into a transmitter that outputs a high-frequency current with a frequency of 25 kHz at an output of 20 kW, and a heating element that passed cooling water of 28 kg at 2.5 kg / cm ² into the pipe was used. A mold having a projected area of 180 × 200 was mounted and connected at a position of 10 mm in the thickness direction from the inner surface of the cavity, and the mold was attached to a press molding machine having a maximum mold clamping force of 100 ton.

First, the output of the transmitter is controlled by the mold to keep it at 100 ° C. and settle to a constant temperature, and then the gel polymer is charged to
After holding at the molding pressure of 25 kg / cm ² for one minute, the output of the transmitter was increased to start the temperature rise and at the same time, the pressure was gradually increased to the final molding pressure of 200 kg / cm ² . In addition, the mold temperature rises at the same time, and when the temperature reaches 160 ° C in 30 seconds, the output of the transmitter is suppressed to the extent that heat dissipation is suppressed and the output is stopped for 3 and 4 minutes at 160 ° C. When the temperature was cooled to 110 ° C, the mold was opened and the molded product was taken out. The residual double bond amount of the obtained molded article, and 130
The surface roughness before and after the post-polymerization at 5 ° C. for 5 hours and 10 hours were measured and shown in Table 1.

Examples 5 and 6 The same molding as in Example 1 was performed except that the maximum temperature of 160 ° C. was 140 ° C. and the holding time at this temperature was 3 minutes and 4 minutes and 1 minute and 2 minutes. The amount of residual double bonds of the obtained molded product and the surface roughness before and after the post-polymerization at 130 ° C. for 10 hours were measured and are shown in Table 1.

Comparative Examples 1 to 4 In Example 1, with the mold temperature kept constant at 130 ° C., the molding pressure after filling the partially crosslinked gel polymer was increased stepwise from 35 kg / cm ² to 200 kg / cm ^2, and 6.5 minutes after material filling. After holding for 20 minutes, it was cooled to obtain a molded product. The residual double bond amount of the obtained molded product and 130 ° C. for 5 hours and 10
The surface roughness before and after the post-polymerization for a certain period of time was measured and is shown in Table 1.

Comparative Example 5 The same molding as in Example 1 was performed except that the holding time at 160 ° C. was 1 minute. The amount of residual double bonds of the obtained molded product and the surface roughness before and after the post-polymerization at 130 ° C. for 10 hours were measured and are shown in Table 1.

Example 7, Comparative Example 6 5 mm obtained in the same manner as in Example 1 except that the maximum temperature of 160 ° C. was 140 ° C. and the holding time at this temperature was 4 minutes.
Thick molded product, and mold temperature 130 ° C. in Example 1
Molding pressure after filling partially crosslinked gel polymer as constant 35 kg / cm
^After gradually increasing from ² to 200 kg / cm ² 6 after filling the material
The amount of the residual double bond of 3 mm thickness of each part was measured for the molded product of 5 mm thickness obtained by holding for 5 minutes and then cooling, and the result is shown in FIG.

Examples 8 to 10 Molding was performed in the same manner as in Example 7 to obtain molded products having a thickness of 4 mm, 6 mm and 8 mm. When the residual double bond amount of 3 mm thickness of each part of this molded article was measured, the same distribution of residual double bond amount as in Example 7 was obtained.

Example 11 80 parts by weight of methyl methacrylate, 20 parts by weight of 2,2-dimethylolpropane dimethacrylate, 1,4
(8) -P-menthadiene 0.1 g / kg, 2,2'-azobis (4-methoxy-2,4-dimethylolvaleronitrile 0.03 g / kg, di-t-butylperoxy-exahydroterephthalate 0 0.5 g / kg and g-t
The mixture obtained by mixing and dissolving 3 g / kg of -butyl peroxide was polymerized for 4 hours by the method of Example 1 to obtain a partially crosslinked gel polymer having a gel fraction of 45%. A partially crosslinked gel polymer kneaded in the same manner as in Example 1 was obtained. On the other hand, in advance, Example 1
In a mold heated to 135 ° C. in the equipment used in Example 1, 60 parts by weight of caprolactam-modified dipentaerythritol hexaacrylate (DPCA-20 manufactured by Nippon Kayaku), 20 parts by weight of trisacryloyl cyanurate, 1,6-hexanediol diacrylate After spray-coating a scratch-resistant layer forming material consisting of 20 parts by weight of acrylate, 20 parts by weight of methyl methacrylate, 1.0% by weight of benzoyl peroxide, and 4.0% by weight of t-butylperoxyisopropyl carbonate, and polymerizing for 45 seconds. After dropping the output of the transmitter and setting the mold temperature to 110 ° C., the gel polymer was charged and the mold was clamped. The mold was opened by cooling to 100 ° C., and the molded product was taken out and polymerized at 130 ° C. for 10 hours to obtain a test sample. FIG. 2 shows the results of changes over time in the scratch resistance due to accelerated exposure.

Comparative Example 7 A test sample was prepared in the same manner as in Example 5 except that the same partially crosslinked gel polymer and scratch resistant layer forming material as in Example 11 were used and molding was performed at a mold temperature of 135 ° C. for 20 minutes. Obtained. FIG. 2 shows the results of the time-dependent change of the scratch resistance performance by the accelerated exposure route.

(Effect of the invention) As described above, the methacrylic resin molded article obtained by the present invention has an average thickness of 0.3 mm centered on a portion having a depth of 0.9 to 1.0 mm from the surface. Since the residual double bond amount is 4.5% or less, and the average residual double bond amount is substantially equal to or decreases from the depth range toward the surface, deformation during use and surface appearance It is a molded product with excellent transparency and heat resistance that does not change. Lighting covers that require transparency and heat resistance, automobile parts,
It is useful for optical parts such as lenses. Further, in the case of the molded product of the present invention, a product obtained by polymerizing and solidifying an acrylic scratch-resistant film at the same time as molding has an effect of improving a decrease in scratch resistance when the coating film is exposed.

[Brief description of drawings]

FIG. 1 is a drawing showing the distribution of the residual double bond amount of 3 mm thickness of each part of the molded products obtained in Example 7 and Comparative Example 6 according to the present invention, showing the distribution of the curing degree in the plate thickness direction, and FIG. 5 is a drawing showing changes over time in scratch resistance performance of a molded article obtained in Example 11 and Comparative Example 7 and a commercially available scratch resistance imparting plate in an ultraviolet accelerated exposure test.

Claims (1)

[Claims] 1. An unsaturated monomer (A) 1 which is mainly composed of alkyl methacrylate and may contain a polymer thereof in a dissolved state.
A desired shape is imparted to the partially crosslinked gel polymer obtained by partially polymerizing 00 parts by weight together with 3 to 100 parts by weight of the crosslinking agent (B) and terminating the polymerization at a gel fraction of 15 to 75%. An article produced by re-polymerization under the following conditions:
The average residual double bond between the monomer having a thickness of 0.3 mm and the cross-linking agent is 4.5% or less, with a portion having a depth of 0.9 to 1.0 mm from the surface of the article as the center, and A methacrylic resin molded article, wherein the average residual double bond amount is substantially equal to or decreases from the depth to the surface.