JPS5921324B2 - Methacrylic San Methyl Cage - Google Patents

Description

Detailed Description of the Invention The present invention involves polymerizing methyl methacrylate or an unsaturated monomer mainly composed of methyl methacrylate while holding it between metal plates to produce a plate-shaped polymer with small internal strain. This invention relates to a method for improving polymerization.

Conventionally, as a method for producing a plate-shaped polymer of methyl methacrylate or an unsaturated monomer mixture containing methyl methacrylate as the main component (hereinafter simply referred to as monomer), the monomer or A sticky mixture containing some polymers (hereinafter referred to as syrup)
The so-called cell casting method is known, in which the polymer is injected and polymerized in a water bath or an air bath. Furthermore, as a method for continuously producing a plate-like polymer, a so-called opposed belt continuous polymerization method is known in which polymerization is carried out between two endless metal belts (US Pat. No. 2,500,728).
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In these polymerization methods, first, the boiling point of the monomer (approximately 100
c) After polymerization at a temperature below, in order to polymerize about 10% of the remaining monomer, it is further heated to a temperature of 100°C or higher to perform so-called curing, so that no strain remains in the polymer. It is usually taken out after cooling down to a certain degree. At this time, in order to prevent the thermal deformation temperature of the polymer from decreasing due to internal strain caused by rapid cooling, a method has been proposed in which the polymer is cooled at a constant rate or less (Japanese Patent Laid-Open No. 49-99187).

Methyl methacrylate exhibits a so-called auto-acceleration effect, in which the polymerization rate increases rapidly once the polymerization has progressed to a certain extent.At this time, there is a sudden generation of heat, and the removal of this heat produces a plate-like polymer with an excellent appearance. necessary to obtain.

If the heat removal is insufficient, the internal temperature will rise and undesirable phenomena such as foaming will occur inside, which will significantly impair the appearance of the obtained polymer. In the case of the cell casting method using glass, the thermal conductivity of glass is low and the thickness is large, so heat transfer is poor and it is difficult to remove rapid heat generation. It is common to polymerize by

In this case, since the cooling rate is slow, the occurrence of internal strain during cooling is not a problem. On the other hand, when a metal cell or metal belt with high thermal conductivity is used, the heat removal rate is high, so that polymerization can be completed at a relatively high temperature and in a short time.

Furthermore, in this case, the cooling rate can be significantly increased, so the time required for cooling can be significantly shortened. However, when the cooling rate is increased, strain remains inside the polymer, which lowers the heat distortion temperature.
Cracks and crazing are likely to occur during solvent bonding, and furthermore, the appearance of the product may be damaged during heat processing.

On the other hand, there is a method disclosed in Japanese Patent Application Laid-Open No. 49-99187, which regulates the cooling rate below a certain rate, but this method cannot fully utilize the advantage of using cells or belts with high thermal conductivity. Moreover, since the cooling rate must be constantly controlled, there is a drawback that the equipment and operation become complicated.

The present inventors have shortened the required cooling time by increasing the cooling rate by taking advantage of the characteristics of the material with good thermal conductivity.
As a result of intensive research into a method that does not leave any strain inside, the present invention was achieved. An object of the present invention is to provide a method for increasing the cooling rate after curing and producing a plate-like polymer of excellent quality.

In the present invention, when producing a plate-like polymer by polymerizing methyl methacrylate or an unsaturated monomer mixture containing methyl methacrylate as a main component while holding it between metal plates, 120 After raising the temperature to ~160°C, it is heated to 110°C at a rate of 25°C or more per minute while being held between metal plates.
Methyl methacrylate or an unsaturated product based on methyl methacrylate, characterized by rapid cooling to 90°C and holding at a selected temperature within that temperature range for at least 1 minute and as short a time as possible. This is a method for producing a polymer of a monomer mixture.

Generally, it is widely known that heat treatment (annealing) is performed at a constant temperature for a certain period of time in order to remove internal strain.

However, in general, annealing is 10 to 15 degrees higher than the heat distortion temperature.
Normally, the process is carried out at a temperature as low as 0.degree. C. for several hours or more, and there is no example in which the process is carried out at a temperature close to or higher than the heat distortion temperature for a short period of time as in the present invention. The method of the present invention is 11
There is an important meaning in cooling to 0 to 90° C. and then holding it for a certain period of time; for example, even if it is once cooled to room temperature and held under the above conditions, the effects of the present invention cannot be obtained.

The cooling rate from 110 to 90°C is preferably as high as possible, but this depends primarily on the cooling method employed.

For example, when placed in a liquid at a specified temperature, the temperature increases at 100°C per minute.
A cooling rate of approximately 30° C./min or higher can be obtained when forced cooling is performed using cold air. The cooling method is not limited to the above method, and any method can be used. The heat treatment temperature is 90 to 110°C, preferably 9
A temperature of 5 to 105°C is used.

If the heat treatment temperature is higher than 110° C., internal strain may occur again due to the influence of the subsequent cooling rate, and the effect cannot necessarily be expected. Further, when the heat treatment temperature is lower than 90° C., the strain cannot be completely removed unless the treatment is performed for a long time equivalent to conventional annealing. Further, when the temperature is 95 to 105°C, more favorable effects can be obtained in the above matters. There is no problem at all even if the holding time is extended for a long time, but since the purpose of the present invention is to obtain a plate-shaped polymer with an excellent appearance in a short time,
Unnecessarily long processing is not desirable as it defeats the original purpose.

On the other hand, the effect cannot be fully exhibited if the treatment time is shorter than 1 minute.

Therefore, the holding time should be determined to be at least 1 minute and as short as possible, depending on the processing temperature, the thickness of the polymer, process constraints, etc. The metal plate used is 0.5
u or more, has sufficient strength to be used as a cell or belt, and has sufficient thermal conductivity, specifically 10 kcal/M. hr. A temperature around ℃ is sufficient.

In the method of the present invention, there are no restrictions on the polymerization conditions before curing, and all conventionally known conditions can be applied.
That is, as the polymerization initiator, one type or a mixture of two or more types of free radical initiators such as organic peroxides and azo compounds, and redox type initiators can be used.

In addition to methyl methacrylate alone, acrylic esters,
It is also possible to use methacrylic acid esters and mixtures of methyl methacrylate and unsaturated monomers copolymerizable with each other, such as styrene. Furthermore, various additives such as dyes and pigments, stabilizers, and mold release agents can also be added to the extent that they do not impair polymerization. As for the polymerization process, if the metal has a high thermal conductivity, it can be applied to both the cell cast method and the opposed belt type continuous polymerization method. In particular, in order to obtain a plate-like polymer with an excellent appearance, a mirror-polished or plated metal plate or belt is suitable. Specific examples will be shown below using Examples. Example 1 25% by weight of methyl methacrylate polymer with an average molecular weight of 84,000 was dissolved in methyl methacrylate monomer to form a viscous syrup, and 0.06% of azobisdimethylvaleronitrile was added as a polymerization initiator. After adding % by weight and thoroughly degassing under reduced pressure, it was placed between two 1.5 mm thick mirror-finished stainless steel cells whose surroundings were sealed with a gasket, and a thermocouple was inserted inside to measure the internal temperature. After adjusting the cell spacing so that the thickness of the obtained polymer was 3 mm,
The mixture was reacted in a 0°C water bath for 25 minutes, then in a 140°C air bath for 20 minutes, and then immediately placed in a 98°C water bath.

As a result, the temperature of the polymer increases from 140°C to 1°C in about 15 seconds.
The temperature decreases almost linearly to 00°C. After maintaining this temperature for 3 minutes, the polymer was taken out, forcedly cooled with air at room temperature, and when the polymer temperature reached 80°C, it was taken out from the cell.

A plate-like polymer with a smooth surface was obtained. The average molecular weight of this material is approximately 750,000, the heat distortion temperature measured by the method of ASTM D648-56 is 95.5°C, and the residual monomer is 1.
．． It was 0%. Examples 2 to 8 After curing, the heat distortion temperatures and residual monomers of polymers produced under the conditions shown in the table below and other conditions as in Example 1 are shown in the table below.

However, if the heat treatment temperature is 100°C or higher, an oil bath is used instead of a water bath. Comparative Example 1 The curing process was carried out under the same conditions as in Example 1, and immediately after that, it was placed in a 40°C water bath and heated from 140°C to 6°C in about 45 seconds.
The heat distortion temperature of the polymer cooled to 0°C was 84.5°C, and the residual monomer content was 1.3%.

When this polymer was further annealed at 82°C for 2 hours, the heat distortion temperature was 95°C, while when annealed at 95°C for 20 minutes, the heat distortion temperature was 89°C. Comparative Example 2 The curing process was carried out under the same conditions as in Example 1, and then the polymer was allowed to cool to room temperature, and the heat deformation temperature of the polymer taken out after being cooled to 80°C for about 20 minutes was 99°C.

Comparative Example 3 The curing process was carried out under the same conditions as in Example 1, then it was placed in an oil bath at 120°C and held for 5 minutes, and then cooled under the same conditions as in Example 1 until it reached 80°C in about 1.5 minutes. The heat distortion temperature of the polymer taken out after cooling was 91°C.

Comparative Example 4 The heat distortion temperature of a polymer produced under the same conditions as in Example 4 except that the heat treatment time was 30 seconds was 89°C.

Claims (1)

[Claims] 1. When methyl methacrylate or an unsaturated monomer mixture containing methyl methacrylate as a main component is polymerized while being held between metal plates to produce a plate-shaped polymer, in the latter stage of the polymerization reaction, 120 After raising the temperature to ~160°C, rapidly cooling it to a temperature of 90 to 110°C at a cooling rate of 25°C or more per minute while being held between metal plates, and during cooling,
A method for producing a methyl methacrylate polymer, which comprises performing a treatment of maintaining a predetermined temperature within the above temperature range for at least 1 minute and as short a time as possible.