JPH0425548A - Acrylic resin composition for injection molding - Google Patents

Abstract

PURPOSE:To significantly improve mold releasability while decreasing the amt. of a mold release agent compounded and thereby avoid the production of a defective injection molded article by molding the title compsn. contg. the mold release agent and a specified amt. of water. CONSTITUTION:The title compsn. contains 0.08wt.% or lower water and 0.03-0.5wt.% at least one mold release agent selected from the group consisting of an 8-30C alkanol, an 8-30C fatty acid, a salt of the acid, and a polyhydric alcohol ester of the acid. The water contained is supposed to affect the adhesion between the surface of a molded article of the compsn. and that of a mold cavity; the higher the water content, the higher the adhesion and the lower the mold releasability of the article.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to an acrylic resin composition for injection molding with excellent mold release properties.

[Prior art]

In recent years, in the field of acrylic resin molding, injection molding is used to obtain molded products with complex shapes such as vehicle meter covers, and to obtain highly precise molded products with ultra-mirror surfaces such as optical lenses and optical discs. Since the adhesion between the molded product and the mold surface is extremely high, an acrylic resin composition with excellent mold releasability is required. In addition, in order to improve productivity during acrylic resin injection molding processing, high-cycle molding processes and robotization are progressing, and improving the mold release properties of acrylic resin is one of the effective means of improving productivity. be.

Conventionally, methods of adding stearyl alcohol, stearic acid, stearic acid metal salts, crystalline paraffin wax, and montan wax to improve the mold release properties of acrylic resins (Japanese Unexamined Patent Publication No. 1983-32298), and methods of adding stearyl alcohol, stearic acid, stearic acid metal salts, crystalline paraffin wax, and montan wax, and methods of adding fluoroalkyl group-containing interfaces Method of adding an activator (Japanese Patent Application Laid-Open No. 58-27737
(Japanese Unexamined Patent Publication No. 1987-73754), a method of adding at least one of esters of polyhydric alcohols and fatty acids, -valent alkyl alcohols, fatty acids, and fatty acid metal salts
, and a method of adding a glycerin higher fatty acid ester and a saturated aliphatic higher alcohol (Japanese Unexamined Patent Publication No. 1-294763).

Although these methods improve the mold releasability of acrylic resin compositions during injection molding to some extent, in recent years, molding of complex shapes required in the field of acrylic resin molding, high-precision molding of ultra-mirror surfaces, In order to improve the productivity of molding processes, it is necessary to mix multiple mold release agents, which can cause silver streaks on molded products, decreased transparency, coloring, surface stains due to bleed-out, and decreased heat transformation temperature. It is easy to cause defects, and further improvements are necessary.

[Problem to be solved by the invention L2] As a result of intensive research into acrylic resin compositions with excellent mold releasability and injection molding methods thereof, the present inventors surprisingly found that the water content of acrylic resin compositions It was discovered that by controlling the amount below a certain critical value, mold releasability can be significantly improved, the amount of mold release agent added can be reduced, and defects in injection molded products can be prevented. However, the present invention was achieved.

[Means to solve the problem]

That is, the present invention contains a mold release agent and has a water content of 0.08. This invention relates to an acrylic resin composition for injection molding that has an excellent mold release property of 1% or less.

In the present invention, although the mechanism by which the moisture content of the acrylic resin composition affects mold releasability during injection molding is unknown, moisture affects the adhesion between the acrylic resin composition molded product and the injection mold surface. However, it is presumed that as the water content of the acrylic resin composition increases, the adhesion increases2 and the mold releasability decreases.

Conventionally, in the field of injection molding, there has been no knowledge regarding the water content of resin and the releasability of molded products, and the present invention is based on a completely new idea.

In the present invention, the water content of the acrylic resin composition is set to 0 so that sufficient mold release properties can be obtained even with a small amount of mold release agent that does not cause defects such as silver streaks on the injection molded product. .0
81Ei 1% or less, preferably 0.06Ei 1% or less, more preferably 0.04IEi 1% or less.

The water content of the acrylic resin composition is 0.0811! When the V% exceeds λ, a large amount of mold release agent must be added to obtain sufficient mold release properties, which is undesirable because defects such as silver streaks are likely to occur in the injection molded product.

The saturated moisture content of acrylic resin is as high as approximately 2%, so
Conventionally, acrylic resin compositions have been packaged using polyethylene inner bags having a thickness of 100 to 200 microns in order to prevent water absorption. Even so, it absorbs moisture during storage, and its moisture content tends to reach 0.2% by weight or more.

If an acrylic resin composition that has absorbed moisture is directly injection molded, defects such as silver streaks and bubbles will occur in the molded product, so conventionally, prior to injection molding, preliminary drying is performed using an air ring hot air dryer, hopper dryer, etc. was. However, in order to prevent the occurrence of the above defects, the degree of drying must be reduced to a moisture content of approximately 0.1 to 0.2! Preferably about 0.1! It was thought that it was sufficient to use it at a low percentage. Therefore, as in the present invention, the water content of the acrylic resin composition is set to 0.08%.
The idea used below did not exist.

In order to keep the moisture content at 0.08% or less, drying conditions must be selected more strictly and carefully. However, the drying method itself can be performed using a conventionally known method.

In the present invention, the moisture content is measured using a Karl Fischer moisture meter (Mitsubishi Kasei Model M (J CA-02 model, MCI).
VA-02 type: heating furnace temperature: 230''C).

The acrylic resin composition of the present invention is selected from the group of monohydric alkyl alcohols having 8 to 30 carbon atoms, fatty acids and metal salts thereof having 8 to 30 carbon atoms, or esters of polyhydric alcohols and fatty acids having 8 to 30 carbon atoms. At least one type of mold release agent
．． 03-0.5 curvature%, preferred, <0.05-0.
This is an acrylic resin composition containing 7% triple lid.

As a monohydric alkyl alcohol having 8 to 30 carbon atoms,
Examples include lauryl alcohol and stearyl alcohol. Examples of fatty acids having 8 to 30 carbon atoms and metal salts thereof include lauric acid, stearic acid, and calcium salts and barium salts thereof. In addition, esters of polyhydric alcohols and fatty acids having 8 to 30 carbon atoms include palmitic acid monoglyceride, stearic acid monoglyceride, hydroxystearic acid monoglyceride, behenic acid monoglyceride, oleic acid monoglyceride, lyric acid monoglyceride, stearic acid diglyceride, and sorbitan laurate. Examples include ester, sorbitan palmitate ester, sorbitan stearate ester, sorbitan oleate ester, polyoxyethylene glycerol monostearate, and the like. In particular, stearic acid,
Preferably, stearic acid monoglyceride or a combination of stearic acid monoglyceride and stearyl alcohol is used.

When the mold release agent content is 0.03% by weight, the molded product tends to have insufficient mold release properties, and when it exceeds 0.5% by weight, defects such as silver streaks may occur in the molded product. This is not preferable because it makes it easier.

In the present invention, in the case of alcohol, fatty acid, and fatty acid ester, the amount of mold release agent blended in the acrylic resin composition was analyzed by ordinary GC analysis (trimethylsilylation was performed in some cases).

Metal salts of fatty acids were determined by atomic absorption spectrometry and GC analysis after reflux extraction and methyl esterification.

In the present invention, the acrylic resin is a copolymer consisting of methyl methacrylate units as a main component and monomer units obtained by copolymerizing with the methyl methacrylate units. The content of methyl methacrylate units is preferably 60% by weight or more. The copolymerizable monomer units are preferably 1% to 40% ungrooved. If it is less than 1% by weight, thermal decomposition tends to occur during injection molding processing, and if it exceeds 40% by weight, the heat deformation resistance temperature tends to decrease, which is undesirable. For example, acrylic acid, methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, isobutyl acrylate, t-butyl acrylate, 2-ethylhexyl acrylate, lauryl acrylate, cyclohexyl acrylate, acrylic acid- Acrylic acid or acrylic esters such as 1-butylcyclohexyl and benzyl acrylate; methacrylic acid, ethyl methacrylate, propyl methacrylate, butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, methano 1JJL[-2-
Methacrylic acid or methacrylic acid esters such as ethylhexyl, cyclohexyl methacrylate, t-butylcyclohexyl methacrylate, phenyl methacrylate, hensyl methacrylate; styrene, vinyltoluene, α
- Aromatic vinyl compounds such as methylstyrene, monochlorostyrene, dichlorostyrene; cinnamic acid esters such as methyl cinnamate; maleic anhydride; imides such as maleimide and phenylmaleimide; acrylonitrile, methacrylonitrile, etc. I can do it.

Preferred ethylene monomers for the present invention are methyl acrylate, ethyl acrylate, cyclohexyl methacrylate, t-butylcyclohexyl methacrylate, styrene, and maleic anhydride.

The weight average molecular weight of the acrylic resin of the present invention is 50.00
Preferably 0 to 300,000, more preferably 7
It is 0.000 to 200,000. When the weight average molecular weight is less than 50,000, the mechanical properties of the injection molded product tend to deteriorate, and when it exceeds 300,000, the melt viscosity tends to become too high.

The method for producing the acrylic resin of the present invention includes suspension polymerization method,
Conventionally known methods such as emulsion method, solution polymerization method, bulk polymerization method, and cast polymerization method can be used. The polymerization temperature is 0 to 170°C, preferably 50 to 150°C. Oil-soluble polymerization initiators used in suspension polymerization, solution polymerization, bulk polymerization, and cast polymerization include azo compounds such as abbisisobutyronitrile, benzoyl peroxide, lauroyl peroxide, and t-butylperoxy-2-ethyl. Organic peroxides such as hexanoate can be mentioned. As a water-soluble polymerization initiator used in emulsion polymerization,
Persulfates such as ammonium persulfate and potassium persulfate,
etc. can be mentioned.

In the present invention, in order to adjust the average molecular weight of IF5 of acrylic resin, butyl mercaptan, octyl mercaptan, dodecyl mercaptan, thioglycolic acid-2-
Molecules of mercaptans such as ethylhexyl! It can be used as a regulator.

In the present invention, conventionally known techniques can be used to blend the mold release agent into the acrylic resin. Specifically, during polymerization of acrylic resin, a predetermined amount of mold release agent is added to the polymerization system, and a predetermined amount of mold release agent is added to beaded or pelleted acrylic resin, mixed with a mixer, and then processed with an extruder. Examples include a method of heating, melting, and kneading.

Further, in the present invention, it is also possible to add a coloring agent diffusing agent and other additives in consideration of the intended use of the final molded product.

In the injection molding method 7 according to the present invention, an acrylic resin composition that has been heated 7 to a fluid state is injected under pressure into the cavity of a closed mold and solidified within the mold. This is a method of making molded products equivalent to 1.

〔Example〕

The present invention will be described in more detail below with reference to Examples, but the present invention is not limited to these Examples.

In the present invention, the mold releasability of the acrylic resin composition was evaluated by the following method. A 4-stage plate mold as shown in Figure 1 was attached to a 3-ounce injection molding machine, and the molding temperature was set to 2.
50°C1 mold temperature 55°C and injection pressure 1,000k
When molding is performed under conditions of g/cd, cracks, chips, or cracks in the 4-tier plate molded product are considered to be defective products, and the percentage of defective products among all molded products is defined as the defective incidence rate. The defined mold releasability evaluation was performed by pre-molding 20 shots to keep the injection conditions constant, then molding 50 shots.
The defective incidence rate among 50 shots was compared.

In addition, for the evaluation of silver streaks, for the same molded products that were evaluated for mold releasability above, those with silver streaks on the surface are considered to be defective7, and the proportion of defective products among all molded products is calculated as defective. It was defined as the incidence rate.

Examples 1 to 4, Comparative Examples 1 to 3 Pure water 57 oz was added to a polymerization reactor equipped with a stirrer and had a content wt 3 oz.
kg tertiary calcium phosphate 7 as suspension stabilizer 285g
, after dispersing 2.3 g of sodium lauryl sulfate, 37.0 kg of methyl methacrylate, 1 methyl acrylate
．． 0 kg, azobisisobutyronitrile 57 g and n
- A mixed solution consisting of 99 g of octyl mercaptan was added, and a mixture was carried out at 80°C with stirring. Next, the polymerization system was cooled to room temperature, and the contents were filtered, washed with water, and dried to obtain a colorless bead-like polymer.

The obtained bead-like polymer was pelletized using a Ghent-type twin-screw extruder with a screw diameter of 30 mm. At this time, stearic acid monoglyceride and stearyl alcohol were added to the bead-like polymer as a mold release agent. 0 each.
It was carried out by blending 10jlE tsumugi% each. The pelleted acrylic resin composition was stored for about two months in a paper bag with a polyethylene inner bag of 100 microns in thickness, but the moisture content of the composition increased to 0.25%.

Thereafter, the moisture-absorbed acrylic resin composition was pre-dried at 60° C. for a predetermined time using a vacuum dryer, and the release weight and water content of the acrylic resin composition were as shown in Table 1. Table 1 shows the incidence of mold releasability defects and the incidence of silver streak defects for these acrylic resin compositions.

Example 5 The polymerization was carried out in exactly the same manner as in Examples 1 to 4, except that the monomers used for polymerization were changed to 31 kg of methyl methacrylate, 1 kg of methyl acrylate, and 6 kg of t-butylcyclohexyl methacrylate. The results are shown in Table 1.

When the water content of the acrylic resin composition is within the range of the present invention, the incidence of mold releasability defects and the incidence of silver streak defects are low.

The following margins Examples 6 to 11, Comparative Examples 4 to 6 Methyl methacrylate 68 parts by weight, Methyl acrylate 2
A mixed solution consisting of 30 parts by weight of ethylbenzene, 0.03 parts by weight of L l-ditertiary-butylperoxy 3,3.5-trimethylcyclohexane and 0.08 parts by weight of n-octylmercaptan was sealed in a total volume of 101 parts by weight. Continuously supplied to a type pressure vessel, average temperature 100℃,
After polymerization with an average residence time of 2 hours, volatile power is removed by reducing the pressure in a storage tank connected to the polymerization reaction tank, and the product is continuously transferred in a molten state to an extruder.

Here, a predetermined amount of mold release agent was quantitatively fed from an additive inlet connected to the extruder to obtain a pellet-shaped acrylic resin composition.

The obtained composition was conditioned and pre-dried in the same manner as in the previous example, and was subjected to evaluation of the incidence of mold releasability defects and the incidence of silver streak defects. The results are shown in Table 2. When the water content of the acrylic resin composition was within the range of the present invention, the incidence of mold releasability defects and the incidence of silver streak defects were low.

〔Effect of the invention〕

According to the present invention, the mold release properties of acrylic resin compositions are significantly improved. Moreover, it becomes possible to reduce the burden of using a mold release agent, and it is possible to prevent defects in injection molded products.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of a mold and its evaluation method for evaluating the mold releasability of an acrylic resin composition in the present invention. Patent applicant: Asahi Kasei Industries, Ltd.

Claims (1)

[Scope of Claims] 1. An acrylic resin composition for injection molding, which contains a mold release agent and has a water content of 0.08% by weight or less. 2(a) Monohydric alkyl alcohol having 8 to 30 carbon atoms, (
b) At least one type of mold release agent selected from the group consisting of fatty acids having 8 to 30 carbon atoms and metal salts thereof, and (c) esters of polyhydric alcohols and fatty acids having 8 to 30 carbon atoms.
An acrylic resin composition for injection molding, which contains 0.03 to 0.5% by weight and has a water content of 0.08% by weight or less.