JPH09151269A - Foamable vinyl chloride resin composition for injection molding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a foamable vinyl chloride resin compsn. for injection molding which can give a foam expanded twice or higher even with an ordinary injection molding machine by compounding a vinyl chloride resin with a specific polymethyl methacrylate resin and a thermally decomposable blowing agent. SOLUTION: This compsn. is prepd. by compounding 100 pts.wt. vinyl chloride resin having an average degree of polymn. of 400-1,000 with 2-30 pts.wt. polymethyl methacrylate resin having a wt. average mol.wt. of 4,500,000-7,000,000 and 0.5-10 pts.wt. thermally decomposable blowing agent. Since the latter resin disperses homogeneously in the former, the melt viscosity of the compsn. is maintained properly without causing excessive heat build-up, enabling a foam with uniform cells to be obtd.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a foamed vinyl chloride resin composition for injection molding, which can be used as a molding material for a general-purpose ordinary injection molding machine.

[0002]

2. Description of the Related Art Molded articles made of vinyl chloride resin are excellent in physical properties such as impact resistance and heat resistance and chemical properties such as solvent resistance, acid resistance and alkali resistance. It has been widely used for other purposes, but since it became possible to mold foam, its characteristics were utilized to make it lightweight, heat insulating,
It has come to be used in applications that require sound insulation,
It is used for a wider range of purposes.

Such a foamed molded product made of a vinyl chloride resin has been manufactured mainly by an extrusion molding method using a pyrolytic inorganic foaming agent, a pyrolytic organic foaming agent or the like. For example, in Japanese Examined Patent Publication No. 63-9540, a vinyl chloride resin having a low degree of polymerization is used as a main material, and as a foaming agent, a thermally decomposable organic foaming agent such as azodicarbonamide and a thermally decomposable type such as sodium bicarbonate. Combined with an inorganic foaming agent, the molecular weight is 20
A highly foamable vinyl chloride resin composition containing 1 to 3 million methacrylic acid ester-based resins and one or more fillers selected from the group consisting of calcium carbonate, talc, clay, asbestos and silica is described. ing.

It has been disclosed that when molded using this resin composition, a foamed molded product having a uniform and fine cell structure, an excellent surface gloss and a skin layer having a high surface hardness can be obtained. However, when the resin composition is molded by an injection molding method, the molten resin is likely to be overheated and thermally decomposed due to retention of the molten resin based on the characteristics of the injection molding method itself, high shearing force, and other reasons. It was difficult to obtain a molded product having a foaming ratio of more than double.

Therefore, a foamed vinyl chloride resin composition suitable for injection molding has been developed. As one of them, JP-A-3-146534 discloses that a vinyl chloride resin having a low degree of polymerization is also used as a main material, and a plasticizer, an impact-resistant agent, and a specific foaming agent are mixed in specific proportions. The following composition is disclosed, and at the same time, a proposal has been made on a rigid vinyl chloride resin foam molded article obtained by using this composition as a material and a method for producing the same.

However, in order to obtain a rigid vinyl chloride resin foam molded article using this technique, as described in the above publication, a special injection molding machine is used and molding is performed under specific molding conditions. It is necessary to use a general-purpose injection molding machine that is widely used.
Dispersion of foam cells is uneven, sink marks occur, etc.
There was a problem in that good quality could not be obtained and the expansion ratio was also lowered.

[0007]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned problems of the prior art, and even a general-purpose ordinary injection molding machine can form a foam having a high expansion ratio of more than 2 times. It is an object of the present invention to provide a foamed vinyl chloride resin composition for injection molding, which is capable of obtaining a molded product which is excellent in quality such as appearance.

[0008]

The foamed vinyl chloride resin composition for injection molding according to the present invention is "2 to 30 parts by weight of polymethylmethacrylate resin having a molecular weight of 4.5 million to 7 million per 100 parts by weight of vinyl chloride resin. Parts and a pyrolytic foaming agent in an amount of 0.5 to 10 parts by weight. "

The vinyl chloride resin used in the present invention may be any one that has been conventionally used as a material for foamed molded articles, for example, a homopolymer of vinyl chloride monomer; Copolymer of vinyl chloride monomer and polymerizable monomer other than vinyl chloride monomer; Graft copolymer obtained by grafting vinyl chloride monomer on polymer other than vinyl chloride resin; or these Examples thereof include a chlorinated vinyl chloride polymer obtained by post-chlorination using a conventionally known method such as a dry method or a wet method. Further, a mixture of these polymers and copolymers is also included.

If the average degree of polymerization of the above vinyl chloride resin is too small, the mechanical strength of the molded product, especially the impact resistance, will decrease. On the contrary, if it is too large, the melt viscosity at the time of molding becomes high, the molding temperature becomes high, the shear heat generation becomes intense, the injection molding becomes difficult, and the foaming failure may occur. Therefore, it is preferably 400 to 1000, and more preferably 500 to 800.

The polymerizable monomer other than the vinyl chloride monomer is not particularly limited as long as it has a reactive double bond and can be copolymerized with the vinyl chloride monomer. , Α-olefins such as propylene and butene-1; vinyl esters such as vinyl acetate and vinyl propionate; vinyl ethers such as butyl vinyl ether and cetyl vinyl ether; acrylic acid esters such as methyl acrylate and ethyl acrylate; methyl methacrylate, Methacrylic acid esters such as ethyl methacrylate and phenyl methacrylate; aromatic vinyls such as styrene and α-methylstyrene; vinyl halides such as vinylidene chloride and vinyl fluoride; N such as N-phenylmaleimide and N-cyclohexylmaleimide -Substituted maleimides and the like, These may be used alone and two or more kinds may be used in combination.

The polymer other than the vinyl chloride resin used in the above graft copolymer is not particularly limited, and examples thereof include ethylene-vinyl acetate copolymer, ethylene-vinyl acetate-carbon monoxide copolymer, ethylene. -Ethyl acrylate copolymer, ethylene-ethyl acrylate-carbon monoxide copolymer, ethylene-methyl methacrylate copolymer, ethylene-propylene copolymer, acrylonitrile-butadiene copolymer, polyurethane, chlorinated polyethylene, chlorinated polypropylene And the like, and these may be used alone or in combination of two or more kinds.

Examples of the polymethylmethacrylate resin used in the present invention include polymethylmethacrylate or methylmethacrylate as a main component, and a copolymer of this with ethylacrylate, acrylonitrile, styrene and the like. The weight average molecular weight of the polymethylmethacrylate resin is limited to 4.5 to 7,000,000, and the use ratio thereof is limited to 2 to 30 parts by weight, preferably 5 to 100 parts by weight of the vinyl chloride resin. Two
0 parts by weight.

If the weight average molecular weight of the polymethylmethacrylate resin is less than 4.5 million, an effective expansion ratio cannot be obtained. Conversely, if it exceeds 7 million, molding of the polymethylmethacrylate resin will occur. At times, not only the dispersion in the vinyl chloride resin becomes poor and the effect of improving the foamability decreases, but not only the melt viscosity becomes high and the moldability deteriorates, but it can be produced industrially. It becomes difficult gradually.

When the amount of the polymethylmethacrylate resin in the above molecular weight range is less than 2 parts by weight,
If a molded product having an effective expansion ratio cannot be obtained and conversely exceeds 30 parts by weight, the melt viscosity at the time of molding becomes high and molding becomes difficult.

Usually, in extrusion molding, a polymethylmethacrylate resin having a molecular weight of 4,000,000 or less is used in order to stabilize the foamability. However, when a resin having a molecular weight of 4.5,000,000 or more is used, molding due to an increase in melt viscosity occurs. Since the foamability deteriorates with the deterioration of the properties and the occurrence of thermal decomposition, it was hardly used.

As a result of various studies conducted by the present inventors on this point, the resin undergoes a high shear rate at the time of molding by an injection molding machine, so that a polymethylmethacrylate resin having a molecular weight of 4.5 to 7 million can be adopted. I found that. That is, by using those in this range, even if the melt viscosity is increased, the moldability is not affected so much, and the desired foaming ratio can be stably obtained.

Examples of the thermal decomposition type foaming agent used in the present invention include thermal decomposition type inorganic foaming agents such as sodium bicarbonate, ammonium bicarbonate and ammonium carbonate; N, N'-dinitrosopentamethylenetetramine, N, N. ′ -Dimethyl-
Nitroso compounds such as N, N'-dinitrosoterephthalamide; azo compounds such as azodicarbonamide and azobisisobutyronitrile; benzenesulfonylhydrazide,
Pyrolysis type organic foaming agents such as sulfonyl hydrazide compounds such as toluene sulfonyl hydrazide can be mentioned. These thermal decomposition type foaming agents may be used alone or in combination of two or more kinds.

The amount of the heat-decomposable foaming agent added may be variously set according to the expansion ratio and quality characteristics of the desired foamed molded product, but is 0.
It is 5 to 10 parts by weight. If the added amount is less than 0.5 parts by weight, it is difficult to obtain an effective expansion ratio,
Even if the amount is more than 10 parts by weight, such an effect is not obtained and the foaming efficiency is deteriorated, which is uneconomical.

The vinyl chloride resin composition of the present invention contains a heat stabilizer, an antioxidant, an antistatic agent, an ultraviolet absorber in order to improve moldability, heat stability, weather resistance and the like, if necessary. Lubricants, fillers, flame retardants, plasticizers, pigments, paints and the like can be added as appropriate.

Examples of the heat stabilizer include tin-based compounds such as dibutyltin malate and dibutyltin mercapto; organometallic soaps such as calcium stearate, barium stearate and zinc stearate; and lead compound systems such as lead stearate. A heat stabilizer is mentioned.

Examples of lubricants include aliphatic hydrocarbons such as polyethylene wax and paraffin wax; higher aliphatic alcohols such as stearyl alcohol; higher fatty acid such as stearic acid and hydroxystearic acid.
Examples include monoalcohol fatty acid ester such as butyl stearate; polyhydric alcohol fatty acid ester such as glycerin monostearate and glycerin tristearate.

Examples of the flame retardant include halogen flame retardants, phosphorus flame retardants, and metal oxide flame retardants such as antimony trioxide.

In order to mix the above-mentioned respective components, the method adopted in the usual compounding of vinyl chloride resin composition can be directly adopted. That is, for example, the respective components may be added to a mixer such as a Henschel mixer and mixed to uniformly mix them.

[0025] As molding conditions for injection molding using the expanded vinyl chloride resin composition of the present invention, it is necessary to properly control the molding temperature of the injection molding machine, the type of resin and foaming agent, and the like. since somewhat with an amount added, can not be said sweepingly, the cylinder temperature, supply temperature (hereinafter referred to as C ₁₎ is 80 to 160 ° C., central temperature (hereinafter C
₂ ) is 100-180 ℃, discharge side temperature (hereinafter C ₃
Is 130 to 200 ° C, the temperature of the nozzle head is 130 to 200 ° C, and the mold temperature is 20 to 80 ° C.
C. is preferred.

(Function) The foamed vinyl chloride resin composition for injection molding of the present invention uses a vinyl chloride resin, polymethylmethacrylate, and a thermal decomposition type foaming agent. Particularly, polymethylmethacrylate has a molecular weight of 4.5 million. Since a specific amount of ~ 7 million is used in a specific amount, foam molding by a normal injection molding machine is possible, and polymethylmethacrylate is uniformly dispersed in the vinyl chloride resin,
The melt viscosity of the molding material is appropriately maintained, the foam cells can be made uniform without excessive heat generation, and an effective high expansion ratio can be obtained.

[0027]

Embodiments of the present invention will be described below in detail.

(Examples 1 to 4 and Comparative Examples 1 to 7) Table 1
A mixture of the various material formulations shown in 1 above was supplied to a Henschel mixer and uniformly mixed to obtain a foamed vinyl chloride resin composition for injection molding. Next, an injection molding machine (manufactured by Japan Steel Works, model: JSWJ100E-C5) was used.
, Inner diameter 32mm, outer diameter 40mm, length 80mm
Into a mold for molding a cylindrical molded body of No. 1 was injection-molded under the following molding conditions to obtain a vinyl chloride resin foam molded body. Various physical properties of the obtained molded product were evaluated by the following evaluation methods, and the results are shown in Table 1.

In Table 1, vinyl chloride resin (I) has an average degree of polymerization of 600, vinyl chloride resin (II) has an average degree of polymerization of 800, and polymethylmethacrylate resin (I) has a molecular weight of 4.7 million ( Mitsubishi Rayon Co., Ltd., trade name: Metabrene P-531), polymethylmethacrylate resin (II) having a molecular weight of 3.1 million (Mitsubishi Rayon Co., Ltd., trade name: Metabrene P-530A), polymethylmethacrylate resin (III ) Has a molecular weight of 1.45 million (trade name: METABLEN P-551 manufactured by Mitsubishi Rayon Co., Ltd.).
A) respectively.

In addition to the vinyl chloride resin and the polymethylmethacrylate resin, the various compounding materials shown in Table 1 also include a thermal decomposition type inorganic foaming agent (trade name: manufactured by Eiwa Chemical Industry Co., Ltd .:
Cerbon SC-D) 4 parts by weight, filler (manufactured by Shiraishi Industry Co., Ltd.,
Trade name: CCR) 5 parts by weight, tin stabilizer (manufactured by Sansha Machine Co., Ltd., trade name: ONZ-142F) 2 parts by weight, polyethylene wax (manufactured by Mitsui Petrochemical Co., Ltd., trade name: Hiwax4)
202E) 1 part by weight, glycerin monostearate (manufactured by Riken Vitamin Co., trade name: RIKEMAL S-100) 1 part by weight, ester lubricant (manufactured by Riken Vitamin Co., trade name: S)
L-02) 0.5 part by weight was blended.

The molding conditions were set as follows.・ Molding temperature C ₁ = 170 ° C., C ₂ = 175 ° C., C ₃ = 180 ° C., nozzle head = 185 ° C. ・ Screw rotation speed = 15%, ・ Injection speed = 70%,
・ Injection pressure = 70% ・ Holding pressure = 0%, ・ Back pressure = 5%, ・ Mold temperature = 40 ° C ・ Injection time = 10 seconds, ・ Cooling time = 60 seconds ・ Measurement = Amount completely filled with resin (Changed depending on the expansion ratio, etc.).

The evaluation method is as follows. Foaming ratio The apparent density of the foamed molded product obtained was determined according to ASTM-D-15.
It measured based on 65 and calculated by the following formula based on the measured value. Foaming ratio = Apparent density of non-foaming resin composition / Apparent density of foamed molded product Foamed cell state The cross section of the foamed molded product was observed with an optical microscope and evaluated according to the following criteria. ○ = cells are evenly distributed, △
= Slightly non-uniform cell distribution state == Non-uniform cell dispersion state Appearance The appearance of the foamed molded product obtained was visually observed and evaluated according to the following criteria. ○ = No sink mark, △ = Slight sink mark, × = Large sink mark

[0033]

[Table 1]

As is clear from the results shown in Table 1, in the case of each example in which a suitable amount of polymethylmethacrylate resin having a molecular weight in a specific range was blended with vinyl chloride resin, the desired quality was obtained. On the other hand, in the cases of Comparative Examples 1 to 3 and 5 in which the polymethylmethacrylate resin having no specific range of molecular weight was used, the expansion ratio was less than 2 times, In case of 5,
A foamed cell with a poor dispersion state was obtained.

Although the same polymethylmethacrylate resin as in Example was used, but in the case of Comparative Example 4 in which the amount used was small, the desired expansion ratio could not be obtained, and the dispersed state of the foam cells was not preferable either. , Comparative Example 6 which also uses a small amount
In the case of No. 2, the expansion ratio was extremely low, the dispersed state of the foam cells was poor, and the appearance shape was not preferable.
Further, in the case of Comparative Example 7 in which the same polymethylmethacrylate as that used in Example was used in a large amount exceeding the specific range, the foaming ratio, foamed cell state and appearance shape were all inferior.

[0036]

The foamed vinyl chloride resin composition for injection molding of the present invention uses a vinyl chloride resin, a polymethylmethacrylate resin, and a thermal decomposition type foaming agent, and in particular, the polymethylmethacrylate resin has a molecular weight of Is 4.5 million to 700
Since a specific amount within the specific range of 10,000 is used, a foaming ratio of more than 2 can be obtained even with an ordinary injection molding machine, and a foamed product excellent in quality such as appearance shape can be obtained. . Therefore, the manufacturing cost can be reduced by using the existing injection molding machine, and the range of applications can be expanded.

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Claims (1)

[Claims] 1. 100 parts by weight of a vinyl chloride resin, 2 to 30 parts by weight of a polymethylmethacrylate resin having a weight average molecular weight of 4.5 to 7 million, and 0.5 parts of a thermal decomposition type foaming agent.
A foamed vinyl chloride resin composition for injection molding, which is characterized by containing 10 to 10 parts by weight.