Stabilizers for Chlorine-Containing Resins and Process for Producing the Same

1. Field of the Invention

The present invention relates to a stabilizer for chlorine-containing resins which is non-toxic, which serves to prevent secondary aggregation of the resins while they are being shipped, and particularly which improves the workability of the resins, and further to a process for producing such stabilizers.

2. Description of the Prior Art

Examples of chlorine-containing resins used in this invention include, for example, polyvinyl chloride, most commonly commercially available with a chlorine content of around 56.6 wt%; polyvinylidene chloride, most commonly commercially available with a chlorine content of around 73.2 wt%; a' vinyl chloride-vinylidene chloride copolymer; a vinyl chloride-vinyl acetate copolymer, most generally commercially available with a vinyl acetate content of 0.4 to 40 wt%, more often 0.5 to 20 wt%; a vinyl chloride-ethylene copolymer, most generally commercially available with an ethylene content of 1 to 15 mole % and a mean molecular weight of 700 to 1500; chlorinated vinyl chloride, most generally commercially available with a chlorine content of 60 to 70 wt%, more often 63 to 68 wt%; and chlorinated polyethylene, most generally commercially available with a chlorine content of 25 to 45 wt%. These materials undergo thermal decomposition during molding, and require a stabilizer to prevent such thermal decomposition. As later will be explained in detail, the present invention provides such a stabilizer.

Heretofore, inorganic acid salts, organic acid metal salts, and organic tin compounds have generally been used as such stabilizers.

Many of these stabilizers are toxic, e.g., those which contain lead, and accordingly their use is limited. Recently, non-toxic calcium hydroxide which has thermal stability and is very inexpensive has come into popular use.

However, particulate calcium hydroxide does not have a smooth surface, so that when the particulate calcium hydroxide or a chlorine-containing resin powder containing such particulate calcium hydroxide is shipped, or particularly when it is automatically fed, the calcium hydroxide aggregates (this phenomenon will hereafter be referred to as secondary aggregation). This phenomenon eventually degrades the dispersibility of the calcium hydroxide in the chlorine-containing resin powder, or degrades the quality of molded products made of such a mixture of a higher proportion of the products must be rejected as unacceptable, because the calcium hydroxide migrates to the surface of the molded products or adheres to metal molds.

Various investigations were conducted by the inventors to overcome these drawbacks, and they found that calcium hydroxide coated with a calcium salt of an organic acid can be used as a non-toxic stabilizer for chlorine-containing resins which prevents secondary aggregation while they are being shipped, improves the workability of the resins upon molding to a substantial extent, and imparts long-term thermal stability to the resins.

The primary object of the present invention is to provide a stabilizer for chlorine-containing resins which comprises calcium hydroxide coated with a calcium salt of organic acid.

Another object of the invention is to provide a process for producing such a stabilizer, which comprises reacting calcium hydroxide with an organic acid at a molar ratio of 1: not more than 2, in the presence of a medium and a surface active agent, while heating and stirring.

The term "medium" as is used herein means water or an organic solvent(s). If desired, the water may contain a suspension stabilizer (such as a suspender, dispersant or surface active agent). Examples of "aqueous mediums" include water, an ammonia solution, an aqueous PVA solution, etc. Examples of an organic solvent "medium" includes hydrocarbon solvents such as petroleum ether, cyclohexane, benzene, etc.; alcohol solvents such as methanol, ethanol, propanol, etc.; halogenated hydrocarbon solvents such as trichloroethane, perchloroethane, etc.; ether solvents such as amylphenyl ether, etc.; and ketone solvents such as acetone, methyl ethyl ketone, etc.; and compatible mixtures thereof.

It is believed that calcium hydroxide disperses into an aqueous solution containing a surface active agent in a suspended state rather than dissolving in the aqueous solution

Examples of suitable surface active agents used in this invention include nonionic surface active agents such as polyoxyethylene alkylphenyl ethers, polyoxyethylene alkyl ethers, polyoxyethylene alkyl esters, sorbitan alkyl esters, polyoxyethylene sorbitan alkyl esters, etc.; anionic surface active agents such as fatty acid salts, sulfuric acid esters of higher alcohols, sulfuric acid esters of aliphatic amines or amides, etc.; cationic surface active agents such as aliphatic amines, quaternary ammonium salts, etc.; and mixtures thereof. The surface active agent provides a sufficient effect even in an amount of less than 0.1% based on the total system weight. Surface active agents having an HLB (hydrophilic-lypophilic balance) of 4 to 17 are generally used.

As organic acids useful in the present invention, there can be exemplified monocarboxylic acids (caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, acrylic acid, methacrylic acid, ricinolic acid, etc.), dicarboxylic acid monoesters (monoesters of oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberinic acid, azelaic acid, sebacic acid, etc.), unsaturated dicarboxylic acid monoesters (monoesters of maleic acid, fumaric acid, citraconic acid, mesaconic acid, itaconic acid, aconitic acid, etc.), aromatic monocarboxylic acids (benzoic acid, salicylic acid, etc.), aromatic dicarboxylic acid monoesters (monoesters of phthalic acid, terephthalic acid, etc.), thiocarboxylic acids (thioglyconic acid, mercaptolactic acid, mercaptopropionic acid, etc.), beef tallow hardened fatty acids, fish oil hardened fatty acids, and oxy fatty acids.

The preferred organic acids used in this invention include saturated and unsaturated fatty acids having 10 to 22 carbon atoms, such as capric acid, lauric acid, palmitic acid, stearic acid, arachic acid, oleic acid, ricinolic acid, etc.; dicarboxylic acid monoalkyl esters having 10 to 22 carbon atoms, in which the alkyl moiety thereof has 1 to 4 carbon atoms, such as esters of oxalic acid, succinic acid, adipic acid, azelaic acid, etc.; unsaturated dicarboxylic acid monoalkyl esters having 10 to 22 carbon atoms, in which the alkyl moiety thereof has 1 to 4 carbon atoms, such as esters of maleic acid, fumaric acid, itaconic acid, etc.; monoaromatic monocarboxylic acids such as benzoic acid, salicylic acid, etc.; aromatic dicarboxylic acid monoalkyl esters having 10 to 22 carbon atoms, in which the alkyl moiety thereof has 1 to 4 carbon atoms, such as esters of phthalic acid, terephthalic acid, etc; thiocarboxylic acids such as thioglyconic acid, mercaptolactic acid; and beef tallow hardened fatty acids, fish oil hardened fatty acids and oxy fatty acids, in which the fatty acid has 8 to 32 carbon atoms and mixtures thereof. The most preferred organic acids are stearic acid and palmitic acid. The minimum amount of acid used is generally abut 2% by weight based on the Ca(OH).sub.2, and a preferred range for the acid in the stabilizer is from about 2 to about 10% by weight, based on the weight of the calcium hydroxide.

As a rule, the reaction between calcium hydroxide and the organic acid, e.g., stearic acid, proceeds as follows:

the theoretical stoichiometric molar ratio of calcium hydroxide to stearic acid required for the reaction is 1:2, but when an organic acid at a molar ratio of not more than 2 is reacted with calcium hydroxide in the presence of a medium and a surface active agent, while heating and stirring, the outer surface or "shell" of the calcium hydroxide reacts with the fatty acid to form the corresponding calcium salt with the fatty acid, while the excess calcium hydroxide which does not participate in the reaction remains as a core, whereby the outer surface of the calcium hydroxide is coated with a calcium salt of the organic acid.

The reaction temperature is about 90.degree. to 100.degree. C. The reaction time is usually about 1 hour after the reaction system reaches the above-defined temperature.

In theory, the higher the conversion of the acid into the calcium salt of the organic acid, the higher the efficiency. In practice on a commercial scale, the conversion of acid into the calcium salt of the organic acid seems to be at most about 50% by weight of the acid.

If the thus obtained stabilizer comprising calcium hydroxide coated with a calcium salt of an organic acid is free from secondary aggregation in a hopper conduit during shipping, flows smoothly to enable easy automatic feeding and if it is mixed with a chlorine-containing resin powder, white calcium hydroxide is prevented from migrating to the surface of molded products made be extruding such a mixture or form adhering to metal molds. The stabilizer of this invention can be mixced with stabilizers, fillers, pigments, lubricants, etc., if desired.

The stabilizer is generally added in an amount of 0.5 to 10% by weight of the system it is blended with.

The following Examples illustrate the invention. All processings were conducted at room temperature, atmospheric pressure and all percentages, parts and ratios were by weight, unless otherwise indicated in the following Examples.

1 liter of water and 400 g of calcium hydroxide were placed in a vessel and stirred at 90.degree. C. to form emulsion (A). 50 cc of water, 40 cc of a 25% ammonia solution, 0.4 g of Monogen ET-170 (a product of Daiichi Kogyo Seiyaku Co., Ltd.; a polyoxyethylene alkylphenyl ether surface active agent) and 8 g of stearic acid were placed in another vessel and stirred at 90.degree. C. to form emulsion (B). Emulsion (B) was gradually added to emulsion (A) over a period of 30 minutes, while stirring at room temperature The mixed emulsion was kept at a predetermined temperature ranging from 70.degree. to 100.degree. C., preferably 95.degree. to 100.degree. C., for one hour and thereafter allowed to stand sufficiently to cool, whereupon it was dehydrated by centrifugal separation. (Standing is a simple way to complete the reaction of stearic acid added and calcium hydroxide.) After drying in a conventional manner there was obtained a stabilizer in the form of powdery particles.

2 Grams of this stabilizer was placed in a beaker, and 50 cc of methyl alcohol as a neutral alcohol added thereto. After allowing the mixture to stand at room temperature for 30 minutes with occasional stirring to complete the elution of unreacted stearic acid, the contents of the beaker were filtered in vacuo using a Nutsche funnel and a pressure bottle. The residue was washed three times with methyl alcohol, and all washings were titrated with 0.05 N NaOH to determine the amount of free stearic acid according to the following formula: ##EQU1## f: titer of a 0.05 N sodium hydroxide standard solution (The molecular weight of stearic acid is 275.)

Table 1 shows the amount (%) of free acid based on the starting stearic acid, in the treatments at 70.degree., 80.degree., 90.degree., 95.degree. and 100.degree. C., respectively.

As will be seen from Table 1, the amount of free stearic acid with respect to the starting stearic acid, in the product which can be obtained at a reaction temperature of 70.degree. C.-Example 1 (1)-is 75%, and it assumed that the remaining 25% stearic acid reacted with calcium hydroxide to form calcium stearate. In the case of Examples 1(4) and 1(5), where the reaction temperature was 95.degree. C. and 100.degree. C., respectively, 97.5% and 100%, respectively, of the stearic acid was assumed to have been reacted with calcium hydroxide to be converted into the calcium stearate. It can thus be concluded that the conversion of stearic acid into calcium stearate takes place more easily at 95.degree.-100.degree. C.

Further, the amount of the stearic acid initially added was much less than 2 mols per mole of calcium hydroxide. The use of such a small amount of stearic acid makes it possible to effect a uniform reaction with the calcium hydroxide in the medium, whereby only the outer surface of the calcium hydroxide stabilizer is converted into calcium stearate, with the excess calcium hydroxide not participating in the reaction remaining as a core, thus forming a stabilizer of calcium hydroxide coated with calcium stearate.

In all examples the particle size distribution of the calcium hydroxide used was as follows, in which the defined values refer to the amounts which remain on the sieve size recited.

100 Parts by weight of polyvinyl chloride was mixed with 3 parts by weight of calcium hydroxide treated according to Example 1(5), except for varying the amount of stearic acid as indicated in Table 2. The resulting mixtures were subjected to the Congo Red test at 190.degree. C. based on JIS K 6732. The thermal stability test results are shown in Table 2 as Examples 2(1)-(3).

Comparative Example 1 relates to the case where 3 parts by weight of calcium hydroxide alone was added, and Comparative Examples 2 to 4 relate to the cases where 3 parts by weight of a mere mixture of calcium hydroxide and calcium stearate in an amount proportional to that used in each of Examples 2(1) to (3) was added.

The thermal resistance time in Comparative Example 1, where only calcium hydroxide was added, was 13 minutes, while that in each of Examples 2(1)-(3) where the calcium hydroxide coated with calcium stearate was added (the amount of the stearic acid used for the reaction based on the calcium hydroxide was respectively 2%, 3%, and 5%) was extended (15.10 minutes, 16.30 minutes and 21.50 minutes, respectively).

The thermal resistance times in Comparative Examples 2 to 4 wherein calcium hydroxide and calcium stearate were used in combination in the amounts as indicated in Table 2, respectively correspond to those of Example 2(1) to (3), i.e., 13.00 minutes vs. 15.10 minutes, 13.00 minutes vs. 16.30 minutes and 14.00 minutes vs. 21.50 minutes. These results establish that the use of the "coated" calcium hydroxides of the invention provides longer thermal stability than the use of a mere mixture of calcium hydroxide and calcium stearate as in the Comparative Examples.

A test on flowability was conducted as follows: 50 g each of the coated calcium hydroxides prepared by the method of Example 1(5) and untreated calcium hydroxide were poured into conventional funnels 170 mm tall, the conical top of the funnel being 90 mm tall and 90 mm in diameter across the top, and the tubular section of the funnel extending from the conical top being 80 mm long and having various diameters as shown in Talbe 3. The conical walls of the funnel made an angle of 70.degree. with respect to horizontal. Upon removing the stopper of each funnel, the slump was measured. The results are shown in Table 3.

As is seen from Table 3, the coated calcium hydroxide of the invention has good flowability, totally slumping in funnels of a 15 mm or a larger diameter, while the untreated calcium hydroxide did not slump in funnels of up to 30 mm in diameter.

With specimens similar to the above, the repose angle (angle with respect to horizontal of the slope naturally formed when a powdery substance is heaped) was measured. In the case of the untreated calcium hydroxide, the angle was 53.degree.08', while in the case of the coated calcium hydroxide prepared by the method of Example 1(5) of the present invention, it was 48.degree.11', proving reduced secondary aggregation and improved flowability. Untreated calcium hydroxide has considerable inter-particle friction and also strong inter-particle affinity, which cause formation of secondary aggregation of calcium hydroxide alone, in the course of transportation. On the other hand, the smooth film formed with calcium stearate over the outer surface of calcium hydroxide in accordance with the present invention serves to reduce the secondary aggregation of the particles, and thus provides remarkably improved flowability.

A powdery mixture of 100 parts by weight of polyvinyl chloride, 3 parts by weight of the coated calcium hydroxide of Example 1, 1.5 parts by weight of calcium stearate, 0.7 part by weight of montanic acid ester wax, 0.5 part by weight of low molecular polyethylene (average polymerization degree: 2000) and 0.3 part by weight of a pigment was subjected to an extrusion test with a 90 mm twin screw extruder provided with a 40 mesh screen (between the extruder and the die) and a die for 60 mm diameter plastic pipe.

An identical mixture except for substituting untreated calcium hydroxide for the coated calcium hydroxide was used as a control.

In the case of the control, secondary aggregation of white calcium hydroxide was observed on the surface of the pipe at a rate of one occurrence for every 1 m of pipe length. In the case of the present invention, no such aggregation was observed.

The mixtures were also subjected to independent continuous extrusion to observe the condition of the metal mold and the screen. In the case of the untreated calcium hydroxide, on the third day the screen was plugged with secondary aggregates and, after 7 working days, the mold was removed to discover a brownish solid substance adhered in a 0.5-1 mm thickness over the entire chromium-plated surface of the metal mold. In the case of the present invention, while on the 6th day the screen was found to be plugged with sand, dusts, impurities, cabonaceous materials and the like, it was not plugged with a secondary aggregate, and after 14 working days, the metal mold was removed with no adhesion on the chromium-plated surface thereof.

While the invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof.