JP2001261850A - Methacrylate-based resin sheet and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a methacrylate-based resin sheet, and a method for manufacturing the same, improved in moldability without detriment to its excellent features of the sheet (cost sheet) such as solvent resistance and good appearance. SOLUTION: In the methacrylate-based resin sheet (cost sheet) manufactured by the method, and distances to the center of sheet thickness from the two sheet surfaces are divided, respectively, into five sections of equal widths in the direction of thickness, and then the difference is 10,000 or less between the Mw obtained as the average of the polymer sections that neighbor the center of sheet thickness and the Mw obtained as the average of the polymer sections on both surfaces. The method for manufacturing the said methacrylate- based resin sheet comprises the 1st polymerization process wherein polymerization proceeds in 60-90 deg.C water or the like until the polymerization degree exceeds 50 mass % with the polymerization heat peak not yet reached and the 2nd polymerization process wherein polymerization proceeds in a 20-130 deg.C gaseous atmosphere until the polymerization heat peak is reached.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a methacrylic resin plate having improved moldability, and a method for producing the resin plate.

[0002]

2. Description of the Related Art A method for producing a methacrylic resin plate by cast polymerization (cast polymerization) is disclosed in, for example, JP-A-8-1.
As described in the example of JP-A-51498, a syrup, which is a monomer or a mixture of a monomer and a polymer, is poured into a cell having a space provided between two glass plates and supported by a soft gasket. Then, there is a method of polymerizing and curing in a hot water bath and then heat-treating in a hot-air drying furnace. Further, for example, as described in JP-B-46-41602, a syrup is continuously supplied and polymerized into a space formed by a stainless steel belt and a gasket facing each other, and a resin plate is supplied from a direction opposite to the supply port. There is a way to take out.

[0003] A resin plate produced by such cast polymerization is generally called a cast plate. Then, the present inventors measured the molecular weight distribution in the thickness direction of the polymer constituting the conventional cast plate, and found that the molecular weight at the center of the plate thickness was low and increased toward the plate surface. I was This tendency was the same regardless of the polymerization method using the glass casting method or the stainless steel casting method. Here, as a method of measuring the molecular weight at each point, the cast plate is immersed in an acetone solvent, and gradually dissolved from the plate surface to make the plate thinner,
A method was employed in which a polymer finely divided in the thickness direction was separated and collected, and a weight average molecular weight was measured by a GPC method described later.

[0004] The molecular weight distribution is formed in the thickness direction because the polymerization temperature of the central part of the syrup is higher and the lower the surface, the more the polymerization initiator is decomposed in the central part. It is considered that the molecular weight of the obtained polymer is low, and the molecular weight of the surface portion is high.

[0005]

Such a cast plate is excellent in solvent resistance, good appearance and the like as compared with an extruded plate. It may be considered that the excellent solvent resistance of the cast plate is exhibited by the fact that the molecular weight of the polymer constituting the cast plate is much larger than that of the extruded plate. On the other hand, the cast plate is a material that is much harder to form than the extruded plate because the molecular weight is extremely large, and as described above, there is a large difference in the molecular weight in the plate thickness direction.

An object of the present invention is to provide a methacrylic resin plate (cast plate) having improved moldability. A further object is to provide a method for producing a methacrylic resin plate (cast plate) having improved moldability without impairing excellent properties such as solvent resistance and good appearance of the cast plate.

[0007]

Means for Solving the Problems As a result of intensive studies to achieve the above object, the present inventors have found that when the polymer conversion rate of the syrup is at least 50% by mass and the polymerization exothermic peak does not appear, the cell (First polymerization step) followed by polymerization in a gas atmosphere with poor heat transfer, and a polymerization exothermic peak occurs in this atmosphere (second polymerization step). Step), the difference between the weight average molecular weight of the surface portion and the center portion is 10
It was found that a novel methacrylic resin plate excellent in moldability was obtained, and the present invention was completed.

That is, the present invention relates to a methacrylic resin plate having a residual monomer content of 3% by mass or less and having a diameter of 0.5 mm or more and containing no air bubbles, which is obtained by cast polymerization of a polymerizable material containing methyl methacrylate. When the methacrylic resin plate is divided into five equal portions in the plate thickness direction based on the distance from both surfaces of the plate to the center of the plate thickness, the weight of the divided region adjacent to the center of the plate thickness is determined. The difference between the weight average molecular weight obtained as the average of the union and the weight average molecular weight obtained as the average of the polymers in the divided regions located on both surfaces of the plate is 100,000 or less, a methacrylic resin plate characterized by the following: is there.

Further, the present invention provides a method for producing the above methacrylic resin plate, which comprises a step of injecting a polymerizable raw material containing methyl methacrylate into a mold, wherein the polymer conversion rate of the polymerizable raw material is 50% by mass. %, And a first polymerization step of polymerizing in a warm water bath or shower at 60 to 90 ° C. until the peak of the polymerization exotherm has not yet appeared, and a temperature of 20 to 130 ° C. until the polymerization exothermic peak appears. A methacrylic resin plate comprising sequentially performing a second polymerization step of performing polymerization in a gas atmosphere, a heat treatment step of maintaining the temperature of the resin plate itself at 110 to 140 ° C. for 3 minutes or more, and a cooling step. It is a manufacturing method of.

In the first polymerization step of the method of the present invention, since the heat medium is hot water, heat transfer to the cell is good, and the rate of heat conduction is determined by the heat conduction inside the syrup. Therefore, it is considered that a temperature distribution is formed in which the temperature in the central portion of the syrup is high, and the temperature decreases toward the surface side. Then, as a result, in the first polymerization step, it is presumed that the polymerization progresses faster in the central portion and the molecular weight of the polymer decreases, and the molecular weight increases relatively toward the surface.

In the present invention, in order to reverse the tendency of the distribution in the first polymerization step, the second polymerization step is successively performed. In the second polymerization step, polymerization is performed in a gas atmosphere. Since the gas atmosphere has poor heat transfer to the cell, the rate-limiting step of heat conduction depends on the heat transfer at the boundary between the cell and the heat medium. As a result, the temperature on the surface side of the syrup rises due to heat generated by polymerization, and the temperature difference from the center tends to disappear. That is, since the conversion rate of the polymer in the first polymerization step is lower on the surface side than in the center of the syrup, the rate of conversion to the polymer in the second polymerization step is conversely reduced by the difference. The amount on the front side increases, and the temperature on the front side of the syrup rises due to polymerization heat.

By performing the first polymerization step and the second polymerization step as described above, the difference in the total heat energy between the central part and the surface part of the syrup can be reduced,
As a result, it becomes possible to manufacture a novel methacrylic resin plate having a small distribution of molecular weight in the plate thickness direction.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below.

The polymerizable raw material used in the present invention includes, for example, a monomer composed of methyl methacrylate alone, or a monomer mixture of methyl methacrylate and another copolymerizable vinyl monomer. As the copolymerizable vinyl monomer, for example, methyl acrylate, ethyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate, and the like are preferable. Syrups obtained by partially polymerizing these monomers or monomer mixtures in the presence of a polymerization initiator are also included. At this time, a chain transfer agent may be added as needed. Further, a methacrylic polymer polymerized by a known bulk polymerization method or suspension polymerization method, a monomer composed of methyl methacrylate alone, or a monomer of methyl methacrylate and another copolymerizable vinyl monomer Syrups dissolved in the mixture are also included. However, it is not limited to these. The content of methyl methacrylate in the polymerizable raw material is preferably 50% by mass or more.

The polymerization temperature for producing syrup is 70
The temperature is preferably from about to 120 ° C. The polymerization rate is 10
About 40 mass% is preferable. As the reactor, a conventionally known tubular or tank-shaped reactor can be used.
Further, the production of syrup may be performed by any of a batch method and a continuous method.

When performing cast polymerization for producing a methacrylic resin plate, it is preferable to add a polymerization initiator to the polymerizable raw material. The polymerization initiator is not particularly limited, but may be used alone or in combination of two or more selected from organic peroxides and azo compounds having a 10-hour half-life temperature of 50 ° C to 70 ° C. preferable.
Specific examples include t-hexyl peroxypivalate,
peroxyesters such as t-butyl peroxypivalate and t-butyl peroxyneohexanoate;
Diacyls such as 4-dichlorobenzoyl peroxide and O-methylbenzoyl peroxide; 2,2′-azobis (2,4-dimethylvaleronitrile), 2,2′-azobisisobutyronitrile, 2,2 ′ Azo compounds such as -azobis (2-methylbutyronitrile); Among them, peroxyesters are preferable.

The amount of the polymerization initiator to be added to the polymerizable raw material is 500 ppm to 10000 p in the case of an organic peroxide.
pm is preferable, and 1000 ppm to 7000 ppm
The degree is more preferred. 30 ppm for azo compounds
About 3000 ppm, preferably 50 ppm to 200 ppm.
About 0 ppm is more preferable.

In the present invention, a polymerizable raw material to which a polymerization initiator and the like are added is poured into a mold (cell), and the first polymerization step is performed in a hot water bath or a hot water shower at 60 to 90 ° C. By the first polymerization step, the polymer conversion of the polymerizable raw material is set to 50% by mass or more. The conversion of this polymer is 50
If the amount is lower than the mass%, bubbles may be generated in the polymerizable raw material in the next second polymerization step, and the bubbles may remain in the finally obtained resin plate. Further, the polymer conversion is preferably 60% by mass or more.

In the first polymerization step, it is important to end the step at least before the peak of the exothermic polymerization appears. The polymerization exothermic peak means a point at which the exotherm reaches a maximum value due to the gel effect as the polymerization of the polymerizable raw material proceeds. Specifically, when a thermocouple is inserted into the polymerizable raw material in the cell and the temperature of the polymerizable raw material is recorded, it can be seen that the temperature of the polymerizable raw material rapidly rises and shows a peak, and then gradually decreases. This peak point is defined as a point at which a polymerization exothermic peak appears. If this first polymerization step is performed until a polymerization heat generation peak appears, a large molecular weight distribution is formed in the thickness direction of the resin plate as in the conventional method.

In the first polymerization step, 60-90 ° C.
The polymerization is carried out in a hot water bath or hot water shower. If the temperature of the hot water is lower than 60 ° C., the polymerization rate is low, which is industrially disadvantageous. On the other hand, when the temperature is 90 ° C. or less, production of warm water is easy. Further, the temperature is preferably from 70C to 85C. When a hot water bath is used, it is preferable to stir or circulate the bath so that a temperature distribution does not occur.

In the second polymerization step, the polymerization proceeds in a gas atmosphere at 20 to 130 ° C. Atmosphere temperature is 20 ° C ~ 1
There is no particular limitation as long as it is in the range of 30 ° C. In the second polymerization step, the polymerization temperature rises due to the spontaneous polymerization heat of the polymerizable raw material. Therefore, there is no need to blow air, and it is preferable not to blow air. Further, it is preferable that there is no heat transfer to the cell, and it is not necessary to strictly control the ambient temperature. However, if the ambient temperature is lower than 20 ° C., a cooling means is required, which is industrially disadvantageous. Further, when the temperature is 130 ° C. or more, the temperature of the polymerization exothermic peak becomes too high,
Bubbles may be generated on the resin plate. The ambient temperature is
It is more preferable that the temperature is 30C to 90C.

In the present invention, it is important that the second polymerization step is continued until a polymerization exothermic peak appears. The polymerization exothermic peak can be detected by the above-described method of inserting a thermocouple. When polymerizing under the same conditions, it is not necessary to insert a thermocouple every time. The polymerization rate at the peak of the heat generated by the polymerization is usually 90% by mass or more. The preferred polymerization mode in the second polymerization step is a polymerization mode in which the temperature of the peak of the exothermic polymerization is 120 ° C. to 130 ° C. and the conversion of the polymer at the end of the second polymerization step is 95% by mass or more.

Subsequent to the second polymerization step, a heat treatment step of maintaining the temperature of the resin plate itself at 110 ° C. to 140 ° C. for 3 minutes or more is performed. By this heat treatment step, it is necessary to make the polymer conversion rate 97% by mass or more. When the heat treatment temperature is lower than 110 ° C., the residual monomer is not easily reduced and is not efficient. On the other hand, when the temperature exceeds 140 ° C., the residual monomer increases. This temperature is 120 ° C
It is more preferable that the temperature is 130 ° C. The holding time in the heat treatment step may be maintained until the conversion of the polymer becomes 97% by mass, preferably 98% by mass or more. That is, the residual monomer content of the methacrylic resin plate is 3% by mass or less, and preferably 2% by mass or less. In order to make the conversion of the polymer 97% by mass or more, the holding time is preferably 3 minutes or more, more preferably 5 minutes or more. There is no upper limit for the holding time, but industrially, it is 1
Within hours is preferred.

As the mold (cell) used in the present invention, for example, a mold composed of a plate-like body such as tempered glass, a chrome-plated plate, a stainless steel plate and a soft vinyl chloride type gasket, or running at the same speed in the same direction. For example, there is a mold including a pair of endless belts and a gasket that runs at the same speed as the two endless belts on both sides.

In this polymerization, if necessary,
Additives such as colorants, plasticizers, lubricants, release agents, stabilizers, and fillers may be added to the polymerizable material.

The methacrylic resin plate of the present invention has a small difference in molecular weight between the surface and the center in the plate thickness direction. Specifically, when this resin plate is divided into five equal portions in the plate thickness direction based on the distance from both surfaces of the plate to the center of the plate thickness, the weight of the divided region adjacent to the center of the plate thickness is determined. The difference between the weight average molecular weight obtained as the average of the coalescence and the weight average molecular weight obtained as the average of the polymers in the divided regions located on both surfaces of the plate is 100,000 or less. Further, this difference is preferably 70,000 or less, more preferably 50,000 or less.

Here, the weight average molecular weight obtained as an average is based on the distance from both surfaces of the plate to the center of the thickness of the plate. Therefore, the average molecular weight of the polymer in the two regions on the front side and the back side is used. Is the meaning of

The weight-average molecular weight of each divided region of the methacrylic resin plate is measured by immersing the methacrylic resin plate in an appropriate solvent, gradually dissolving it from the plate surface, and then dissolving the methacrylic resin plate in a predetermined divided region (from both surfaces of the plate). The thickness was reduced to the boundary of each area divided into five equal widths in the thickness direction based on the distance to the center of the thickness. The polymer dissolved in the solvent was recovered for each area, and the weight average molecular weight was obtained. May be carried out by a method of measuring. Specifically, a method adopted in an embodiment described later may be followed.

The methacrylic resin plate of the present invention has a residual monomer content of 3% by mass or less and does not contain bubbles having a diameter of 0.5 mm or more. The residual monomer amount is measured for a region including the entire thickness of the resin plate. Further, the thickness of the methacrylic resin plate of the present invention is preferably in the range of 1 to 12 mm.

[0030]

The present invention will be described in more detail with reference to the following examples. The evaluation in the examples was performed according to the following method.

(1) The recording of the polymerization exothermic peak was performed by inserting a 1.5 mm diameter thermocouple into the syrup through a gasket, measuring the temperature at the time when the maximum temperature in the polymerizable raw material was reached, and recording this. .

(2) The presence or absence of air bubbles in the cast plate was confirmed with the naked eye, and the size was measured using a 30-fold loupe with a length scale.

(3) Measurement of distribution of weight average molecular weight in the thickness direction: A cast plate after polymerization is cut into a 50 mm square, and an aluminum tape (Scotch heat-resistant aluminum tape) is applied so that all sides are covered except for the front and back surfaces. 3M) was used as a sample. This sample was immersed in 200 ml of acetone, left to stand, and when the surface swelled appropriately, the divided regions located on the plate surface among the five divided regions of equal width, that is, the region of the front surface and the region of the back surface of the plate. Was scraped off to the boundary of the divided region, dissolved in acetone, and collected. Then, this sample was immersed again in fresh acetone, and the same operation was repeated five times until only the sides were left and the front and back surfaces were not completely melted. The five kinds of polymers dissolved in each acetone obtained in this way were each treated with n
-The precipitate was reprecipitated in hexane and dried under vacuum to recover only the polymer, and the molecular weight was measured by the GPC method.

(4) Measurement of weight average molecular weight by GPC method: The polymer obtained by the above measurement (3) was dissolved in tetrahydrofuran (THF) at 40 ° C. for 1 hour, and subjected to liquid chromatography manufactured by Tosoh Corporation. HLC-8
Model 020 was used and the separation column was GMH of TSK-Gel.
XL in series, solvent is THF, flow rate is 1.0 ml / mi
n, the detector was a differential refractometer, the measurement temperature was 40 ° C., and the injection volume was 0.1 ml. As standard polymers,
Methacrylic resin was used.

(5) Amount of residual monomer: pulverizing a resin plate,
Dissolve the crushed resin plate (including the whole thickness) in acetone,
Hewlett-Packard gas chromatography:
Using HP-6890 type, the separation column is HP-Wax
(0.25 mm diameter × 30 m length), the measurement temperature was 40 ° C., the detector was FID, and the internal standard was methyl isobutyl ketone.

(6) Comparative evaluation of solvent resistance: A resin plate was immersed in methylene chloride at a temperature of 25 ° C. for 10 minutes, brought into contact with a standard methacrylic resin plate, and air-dried for 1 hour to observe the state of the adhesive interface. did. The ones with many bubbles at the bonding interface
The mark and those that did not occur are marked with a circle.

7. Comparative evaluation of moldability: φ220m
m, using a vacuum forming mold with a depth of 140 mm, the plate temperature 1
Vacuum forming at 40 ° C, bottom corner R of obtained molded product
(Mm) was measured and used as an index of moldability.

[Examples 1 to 3] 2,2 'as a polymerization initiator
-Using azobis (2,4-dimethylvaleronitrile), methyl methacrylate monomer is added at 90 ° C to 103 ° C.
And a part of the mixture is polymerized to obtain a polymerization rate of 2
A polymerizable raw material having 4% by mass and a viscosity of 1.8 Pa · s / 20 ° C. was obtained. The polymerization initiator shown in Table 1, a release agent, an ultraviolet absorber, and a polymerization inhibitor were added to this polymerizable raw material, and the mixture was degassed in vacuum. The syrup was then weighed 1.5 mm, 35
cm × 65cm stainless steel plate or 5mm thick,
Polymerization was carried out by pouring into a casting polymerization cell composed of a 35 cm × 65 cm tempered glass plate, a clip, and a soft vinyl chloride gasket to produce a cast plate having a thickness of 5 mm. The polymerization conditions are shown in Table 1, and the evaluation results of the obtained cast plate are shown in Table 2.

Further, in order to examine the polymer conversion of the polymerizable raw material at the end of the first polymerization step in Examples 1 to 3, the first polymerization step in Examples 1 to 3 was carried out, and then the mixture was rapidly cooled. To determine the polymer conversion. The polymer conversion of the polymerizable raw material at the end of the first polymerization step in each example was 65% by mass on average in Example 1, 63% by mass in Example 2, and 63% by mass on average.
Was 68% by mass on average.

Comparative Examples 1-4 Using the same polymerizable raw materials as in Examples 1-3, cast plates having a thickness of 5 mm were produced under the polymerization conditions shown in Table 1. Table 2 shows the evaluation results. The conversion of the polymerizable raw material at the end of the first polymerization step in Comparative Example 3 was examined in the same manner as in Example. At the end of the first polymerization step, the polymer conversion of the syrup was 42% by mass.

[0041]

[Table 1]

[0042]

[Table 2]

In Examples 1 to 3, the methacrylic resin plate of the present invention in which the difference between the weight average molecular weight of the polymer in the central region and the weight average molecular weight of the polymer in the regions on both surfaces was 100,000 or less was produced. It is an excellent example of the moldability (corner R at the time of vacuum forming). Further, Examples 1 to 3 are examples in which the method of the present invention was carried out, and improved the moldability of the methacrylic resin plate without impairing the solvent resistance and the good appearance.

[0044]

As described above, the methacrylic resin plate of the present invention is excellent in molding workability, and therefore, is extremely useful in industry. Further, according to the method for producing a methacrylic resin plate of the present invention, a methacrylic resin plate having improved moldability can be produced without impairing excellent properties such as solvent resistance and good appearance of a conventional cast plate. Since it is possible, it is more industrially useful.

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Claims (2)

[Claims] An amount of a residual monomer obtained by cast polymerization of a polymerizable material containing methyl methacrylate is 3% by mass.
Hereinafter, a methacrylic resin plate having a diameter of 0.5 mm or more and containing no air bubbles, wherein the methacrylic resin plate has a uniform width in a plate thickness direction based on a distance from both surfaces of the plate to a center of the plate thickness. When each is divided into five, the weight average molecular weight obtained as the average of the polymer of the divided region adjacent to the plate thickness center portion, and the weight average molecular weight obtained as the average of the polymer of the divided region located on both surfaces of the plate A methacrylic resin plate having a difference of 100,000 or less. 2. A method for producing a methacrylic resin plate according to claim 1, wherein a polymerizable material containing methyl methacrylate is injected into a mold, and the polymer conversion rate of the polymerizable material is 50. Mass% or more,
Until the exothermic peak of polymerization has not yet appeared, 60
A first polymerization step of polymerizing in a hot water bath or a hot water shower at 〜90 ° C .; a second polymerization step of polymerizing in a gas atmosphere at 20-130 ° C. until a polymerization exothermic peak appears; A method for producing a methacrylic resin plate, comprising sequentially performing a heat treatment step of maintaining the temperature at 110 to 140 ° C. for 3 minutes or more and a cooling step.