JP2008201854A - Method for producing methacrylic resin - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for stably producing a high-quality methacrylic resin. <P>SOLUTION: The method for producing the methacrylic resin includes using a stainless steel surface-treated with an aqueous solution of a chelating agent as a mold, and polymerizing a polymerizable raw material containing ≥50 mass% methyl methacrylate monomer in the mold. The stainless steel having ≤20 atomic% iron concentration on the surface measured by an X-ray photoelectron spectroscopy is used as the mold, and an aminocarboxylic acid-based chelating agent is used as the chelating agent. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for producing a methacrylic resin polymer using stainless steel as a mold.

  Methacrylic resins have excellent optical properties, weather resistance, and high mechanical properties, so they are widely used in light guide plates and IT equipment in recent years, such as automotive parts, lighting equipment, and OA equipment parts. It has been.

  As a method for producing a methacrylic resin, a suspension polymerization method, an emulsion polymerization method, a bulk polymerization method and the like can be cited as known techniques. Among the facilities for producing these resins, particularly in reaction kettles that carry out polymerization reactions, stainless steel processed by a known manufacturing method is used. It is known that the quality of the resin is not stable. When polymerization is carried out using a reaction kettle, it is uniformly stirred by the stirring blades inside the reaction kettle, so that even if metal ions are eluted, the influence on the polymer is dispersed and the quality is not significantly reduced. Or, there may be an abnormality in polymer formation only in the initial stage of use. Furthermore, as a method for avoiding elution of metal ions, for example, the inner surface of the reaction kettle is glass-treated to prevent elution of metal ions, and a stable polymer is obtained.

  On the other hand, there is a mold plate making method in which syrup containing methyl methacrylate as a main component is injected into a mold made of inorganic glass or stainless steel plate and polymerized in the mold to obtain a plate polymer, which has excellent optical quality and solvent resistance. It has high properties, workability, mechanical strength, etc., and it is widely used in information related fields.

  Compared to the polymerization method using the reaction kettle, in the mold plate method using stainless steel as a mold, it is almost impossible to forcibly stir the injected raw material monomer. It will be in contact with the stainless steel for a long time until it is formed and the polymer is taken out, and the interface between the stainless steel and the polymer tends to be affected by metal ions.

  As a method for efficiently producing a mold plate making method using stainless steel, for example, in Patent Document 1, two continuous belt-like stainless steel surfaces are arranged in the vertical position, the vertical distance, speed, and direction are constant, There is a method in which a continuous gasket is run on both sides of a stainless steel surface, and a liquid raw material obtained by polymerizing a part of the monomer is continuously injected between molds to continuously polymerize. is there.

  The continuous mold plate manufacturing method is more productive than the batch operation mold plate manufacturing method, and can ensure a constant thickness of the plate. Many products can be manufactured by continuous plate making, such as forming a film and laminating a resin on it.

  For example, in Patent Document 2, in this continuous mold plate making method, when the polymerization is completed and the stainless steel mold and the polymer are peeled off, the adhesion between the two may be too strong and the peeling may be promoted. For this purpose, the release agent is mixed with the raw material to improve the release property.

  However, when a large amount of release agent is mixed for the purpose of peeling, the release agent adheres to the surface of the stainless steel mold and causes mold surface contamination, or the release agent attached to the surface of the mold accumulates to cause unevenness on the mold surface. As a result, unevenness may be transferred to the outermost layer of the resin plate, leading to a decrease in quality.

  If the quality of the resin plate deteriorates due to the deposition of the release agent, the surface of the stainless steel mold will be mirror-polished, but the mirror-polishing process will interrupt production and require a longer time. There is.

  On the other hand, when the addition amount of the release agent is lowered, the release of the stainless steel mold and the polymer does not proceed satisfactorily, so that the resin plate is deformed or cracked. In particular, cracks in the resin plate cause scratches on the surface of the stainless steel, and when the scratches are transferred to the surface of the resin plate, the quality of the resin plate is deteriorated or excessively peeled off. Small cracks are generated in the film, resulting in a decrease in optical quality.

  In Patent Document 3, a vinyl monomer containing a methacrylic acid ester is polymerized in the presence of a chelating agent and triphenylphosphine to reduce the influence of iron ions eluted from stainless steel to obtain a methacrylic resin. Yes. In this method, a chelating agent that has an effect on peelability but does not dissolve in the methyl methacrylate monomer is added, so it is difficult to obtain a transparent molded plate. It has been desired to further improve the above.

In the continuous plate making method using a strip-shaped stainless steel mold, a method for improving the peelability from the viewpoint of stabilizing quality and reducing defective products has been desired in production after mirror polishing. As a surface treatment method for a stainless steel sheet, for example, in Patent Document 4, pickling and washing stainless steel with an acid adjusted to pH = 2.5 to 3.5, and selectively dissolving iron in the passive film By eluting iron ions from a method for producing stainless steel having a passive film composed mainly of chromium oxide or hydrate, the iron in the passive film of stainless steel is made 30 atomic% or less. We provide container materials with low contamination. In this method, it is necessary to lengthen the processing time, which is a problem in terms of productivity.
Japanese Patent Publication No. 47-34815 Japanese Patent Publication No. 47-13147 JP 09-136909 A JP 2001-131765 A

  The object of the present invention is to reduce the deterioration of the quality of resin products that occur at the initial stage of production after stainless steel surface polishing in the production of methacrylic resin using stainless steel as a mold, and to provide a stable and high-quality methacrylic resin. A method of manufacturing is provided.

  The present invention is a method for producing a methacrylic resin in which a stainless steel surface-treated with an aqueous chelating agent solution is used as a mold, and a polymerizable raw material containing 50% by mass or more of a methyl methacrylate monomer is polymerized in the mold.

  By treating the stainless steel used as the mold with a chelating agent aqueous solution, it is possible to avoid polymerization failure of the methacrylic resin plate due to elution of iron ions from the surface of the stainless steel, and consequently improve the peelability of the resin plate. it can. In other words, it is possible to avoid troubles due to redox polymerization caused by iron ions at the interface between stainless steel and resin plate, which occurs during the production period after mirror polishing. High methacrylic resin plate can be produced.

In the present invention, a stainless steel surface-treated with an aqueous chelating agent solution is used as a mold, and a polymerizable raw material containing a methyl methacrylate monomer is polymerized in the mold to produce a methacrylic resin.

  A chelating agent is a generic term for compounds that have a structure in which a metal is sandwiched in the center and can coordinate with a metal ion, removing harmful metals, recovering metals from dilute solutions, and from multi-component systems. Used in separation and purification.

  As a chelating agent, for example, as an aminocarboxylic acid-based chelating agent, ethylenediaminetetraacetic acid (EDTA) salt, nitriloacetic acid (NTA), diethyltriaminepentaacetic acid (DTPA), N- (hydroxyethyl) ethylenediaminetriacetic acid (HEDTA), diethylenetriamine Pentaacetic acid (GEDTA), triethyltetraamine hexaacetic acid (TTHA), N- (2-hydroxyethyl) iminoniacetic acid (HIDA), propanediaminetetraacetic acid (PDTA), dihydroxyethylglycerin (DHEG), etc., and phosphonic acid-based chelates As an agent, hydroxyethyldiene diphosphate (HEDP), nitriotrismethylenetetraphosphate (NTMP), tetrakis (phosphonomethyl) ethylenediamine (EDTMP), or the like, or a salt of these structures, Compounds having these structures and the like. The chelating agent in the present invention is not limited to these, but aminocarboxylic acid-based chelating agents are preferable, among which ethylenediaminetetraacetic acid (EDTA) salts are more preferable, and among them, ethylenediaminetetraacetic acid-2 sodium salt (EDTA) -2Na) is particularly preferred. These can be used alone or in combination of two or more.

  The surface treatment in the present invention refers to immersing stainless steel in an aqueous chelating agent solution. 20-90 degreeC is preferable and the immersion temperature to the chelating agent aqueous solution of stainless steel has more preferable 30-70 degreeC. If the immersion temperature is too low, it is difficult to obtain a surface treatment effect. If the immersion temperature is too high, the volatilization of water from the aqueous solution increases, so that crystals of the chelating agent adhere to the interface and the liquid concentration changes. Moreover, 0.1-5 mass% is preferable, the concentration of a chelating agent is more preferable, 0.2-2 mass% is more preferable, and 0.5-1 mass% is further more preferable. If the concentration of the chelating agent is too low, the surface treatment effect is lowered, so that it is necessary to make the immersion time long, or the surface treatment effect may not be obtained, which is not preferable. When the concentration of the chelating agent is too high, the surface treatment effect is not improved, which is disadvantageous in cost. The immersion time in the chelating agent aqueous solution is preferably 1 to 10 hours, and more preferably 2 to 3 hours. If the immersion time is too short, the surface treatment effect is lowered, and if the immersion time is too long, the surface treatment effect is hardly improved. In order to improve the surface treatment effect, the aqueous chelating agent solution is preferably stirred when immersed.

  The material of stainless steel used as a mold in the present invention is not particularly limited, and examples thereof include austenite (SUS304, SUS316, etc.), ferrite (SUS430, etc.), and martensite (SUS403, etc.). Among these, austenite is preferable from the viewpoint of corrosion resistance, and SUS304 is more preferable from the viewpoint of surface polishing processability. The typical composition ratio (%) of SUS304 stainless steel is Fe / Cr / Ni of 74/18/8.

  In the present invention, the iron atom concentration on the surface of stainless steel can be determined by a known method such as analysis using X-ray photoelectron spectroscopy (hereinafter referred to as XPS) which is one of surface analyzers.

  The iron atom concentration on the stainless steel surface in the present invention is preferably 20 atomic% or less.

  If the iron atom concentration is too high, the polymerization of the polymer does not proceed normally due to the influence of iron ions, and peeling at the interface between the methacrylic resin surface and the stainless steel plate tends to be worsened and the quality of the resin surface tends to deteriorate.

  Since stainless steel undergoes air oxidation on the surface immediately after polishing and forms a passive film, the iron concentration (atomic%) does not indicate the content of the entire stainless steel surface even in the measurement by XPS. It is known that iron has a low concentration due to the influence of oxygen.

  The polymerizable raw material used in the present invention is a polymerizable raw material containing 50% by mass of methyl methacrylate, and may be a monomer mixture with other vinyl monomers copolymerizable therewith.

  Other vinyl monomers copolymerizable with methyl methacrylate are, for example, ethyl methacrylate, isopropyl methacrylate, t-butyl methacrylate, s-butyl methacrylate, n-butyl methacrylate, amyl methacrylate, octyl methacrylate, Methacrylic acid esters such as 2-ethylhexyl methacrylate, lauryl methacrylate, phenyl methacrylate, cyclohexyl methacrylate, benzyl methacrylate; methyl acrylate, ethyl acrylate, isopropyl acrylate, butyl acrylate, t-butyl acrylate, Acrylate esters such as amyl acrylate, octyl acrylate, 2-ethylhexyl acrylate, lauryl acrylate, cyclohexyl acrylate, phenyl acrylate, and benzyl acrylate; styrene, α- Vinyl aromatics such as til styrene, paramethyl styrene, isopropenyl styrene and vinyl toluene; unsaturated nitriles such as acrylonitrile and methacrylonitrile; unsaturated carboxylic acids such as methacrylic acid, acrylic acid and maleic anhydride; ethylene glycol di And polyunsaturated compounds such as (meth) acrylate, diethylene glycol di (meth) acrylate, and divinylbenzene. However, it is not limited to these, and these can be used alone or in combination of two or more. Here, “(meth) acrylate” means “methacrylate” or “acrylate”.

  The composition ratio of the monomer that is the raw material of the methacrylic resin of the present invention is 60 to 100% by mass of methyl methacrylate from the viewpoint of maintaining the original physical properties of the methacrylic resin obtained by polymerization, and other copolymerizable with this. The vinyl monomer is preferably 40 to 0% by mass, more preferably 90 to 100% by mass of methyl methacrylate and 10 to 0% by mass of another vinyl monomer copolymerizable therewith.

  In the present invention, the above-described polymerizable raw material is subjected to cast polymerization. Instead of the monomer, a mixture of the monomer and the polymer (hereinafter referred to as “syrup”) is used for the polymerization. There is no problem.

  The polymerization initiator that can be used for the polymerization of the monomer or syrup is not particularly limited, and examples thereof include azo polymerization initiators such as azobisisobutyronitrile and azobisdimethylvaleronitrile, benzoyl peroxide, t- Examples thereof include organic peroxides such as butyl peroxy 2-ethylhexanoate and t-hexyl peroxypivalate.

  In the polymerization, a molecular weight modifier may be used as necessary. Examples of the molecular weight modifier include alkyl mercaptans such as n-butyl mercaptan, n-octyl mercaptan, and n-dodecyl mercaptan.

  The polymerization temperature varies depending on the type of polymerization initiator used, but is preferably 40 to 170 ° C. from the viewpoint of ease of control of the polymerization reaction, productivity, and the like.

  In the polymerization, various additives used in producing a normal methacrylic resin or a modified product thereof can be added. Additives include dyes used for coloring, pigments, antioxidants, stabilizers such as UV absorbers, flame retardants, plasticizers, release agents that easily peel off resin castings from molds, chain transfer agents, crosslinks Agents and the like. However, these additives can contaminate the surface of stainless steel by bleeding out from the resin polymer during the production of the resin polymer, or bind to trace amounts of ions other than iron ions eluted from the stainless steel. Since there is a possibility of coloration or discoloration, the addition amount is preferably kept to a minimum. After polymerization, a methacrylic resin can be obtained by removing the obtained molded product from the mold. The molded product is preferably plate-shaped from the viewpoint of releasability.

Hereinafter, the present invention will be described in more detail with reference to examples. The peelability and surface quality were evaluated by the following methods.

(Peelability)
When the resin plate is peeled off from the mold, ○ is peeled off when force is not required, but is peeled off when the force is required. Δ: Not peeled or difficult to peel, and the resin plate is broken during the peeling. Was evaluated as x.

(Surface quality)
Using a metal halide light source made of MORITEX in the dark room, visually observe the surface quality of the resin plate on the stainless steel plate contact surface side. Evaluated as ○.

[Example 1]
SUS304 stainless steel (surface polished, mirror finished product) for XPS measurement having a plate thickness of 1.6 mm, a width of 450 mm, a length of 600 mm, and a plate thickness of 1.6 mm, a width and a length of 15 mm was used. In order to remove the adhesion of organic matter and dirt on the surface of the stainless steel plate, a pretreatment was performed after washing with acetone, followed by washing with distilled water and air drying.

  10 liters of 1.0 mass% EDTA-2Na aqueous solution was put into a bath in a plastic bathtub, and the above-mentioned two stainless steel plates were immersed in a water bath maintained in a range of 60 ° C. ± 3 ° C. for 3 hours. A circulation pump was attached to forcibly stir the aqueous solution. After the immersion treatment, the product was taken out from the bathtub, washed with warm water and then distilled water, and then air-dried to obtain a methacrylic resin mold.

  The method for determining the iron concentration (atomic%) in the passive film of the surface-treated stainless steel sheet with the chelating aqueous solution was determined as follows. That is, it is assumed that measurement is performed under the conditions of 200 W monochrome X-ray source (AlKα) and Pass Energy 20 eV (narrow scan) by XPS (ESCA LAB220iXL manufactured by VG), and the peak area (integration) value of the obtained Fe is determined as the peak area. The iron concentration (atomic%) is calculated by dividing the (integral) value, the Cr peak area (integral), the Ni peak area (integral), the O peak area (integral), and the C peak area (integral). )

  The prepolymerization of the methacrylic resin was performed using a glass three-necked flask container with a 5 liter internal volume equipped with a cooling tube, a stirring blade, and a jacket on the outside, to which methyl methacrylate monomer was added. The inside and monomer were fully substituted with nitrogen. After the addition of the methyl methacrylate monomer, the mixture was heated, and after the internal temperature reached 80 ° C., 2,2′-azobis (2,4-dimethylvaleronitrile) was added to 100 parts by mass of the methyl methacrylate monomer. 0.05 part by mass was added and held for 10 minutes after reaching the boiling point, and then the inside of the container was cooled to obtain a methacrylate syrup having a polymerization rate of about 22% by mass. Next, after adding 0.25 parts by mass of t-hexylperoxypivalate and 0.005 parts by mass of sodium di (2-ethylhexyl) sulfosuccinate as a release agent to 100 parts by mass of this methacrylic tosyrup, , And degassed under reduced pressure at -90 kPa (gauge pressure) for 5 minutes.

  The syrup obtained by the prepolymerization was poured into a mold composed of a clip and fixed with one sheet of tempered glass of the same size as stainless steel and a polyvinyl chloride gasket arranged between them. After polymerizing and solidifying in an 80 ° C. water bath for 30 minutes, the mixture was subsequently placed in a 110 ° C. air hot air circulating thermostatic bath for 30 minutes for heat treatment.

  After taking out from the thermostat and peeling off the tempered glass quickly, the obtained plate-like molded product (molded plate) was peeled off from the stainless steel plate. The results are shown in Table 1.

[Example 2]
All operations were performed according to Example 1 except that the concentration of EDTA-2Na was changed to 0.5% by mass. The results are shown in Table 1.

[Example 3]
All operations were performed according to Example 1 except that the concentration of EDTA-2Na was changed to 2.0% by mass. The results are shown in Table 1.
[Comparative Example 1]
Except that EDTA-2Na was not added, a resin plate was obtained under the same conditions and techniques as in Example 1, and peeling evaluation was performed. The results are shown in Table 1.

[Comparative Example 2]
The stainless steel was washed and air-dried in the above pretreatment without performing the treatment of Example 1, and then a resin plate was produced under the same conditions, and the peelability was evaluated. The results are shown in Table 1.

As a result of the above examples, the peelability is improved by producing the stainless steel plate after the mirror polishing treatment is immersed in the chelating agent aqueous solution, and a methacrylic resin having a high surface quality can be obtained. did it.

  The methacrylic resin obtained by the production method of the present invention has high quality and is suitable for various uses.

Claims (4)

  A method for producing a methacrylic resin, in which a stainless steel surface-treated with an aqueous chelating agent solution is used as a mold, and a polymerizable raw material containing 50% by mass or more of a methyl methacrylate monomer is polymerized in the mold.   The method for producing a methacrylic resin according to claim 1, wherein a stainless steel whose surface iron concentration measured by X-ray photoelectron spectroscopy is 20 atomic% or less is used as a mold.   3. A stainless steel having a liquid temperature of 20 ° C. to 90 ° C. and a surface treatment by immersion in a chelating agent aqueous solution having a chelating agent concentration of 0.1 to 5% by mass for 1 to 10 hours is used as a mold. The manufacturing method of methacrylic resin of description.   The method for producing a methacrylic resin according to any one of claims 1 to 3, wherein the chelating agent is an aminocarboxylic acid chelating agent.