VINYL CHLORIDE-BASED RESIN COMPOSITION OF LOW MALODOUR

Abstract: A polyvinyl chloride resin composition which is highly heat-resistant as a result of compounding with an organic tin mercaptide compound as a heat stabilizer is still free from the problem of the unpleasant odour emitted by the mercaptide compound as a result of compounding a specific deodorizing agent therewith, so that the composition is suitable as a moulding resin composition for food containers. The deodorizing agent is a diterpenic acid such as abietic acid or a rosin, which latter is a crude mixture of several kinds of diterpenic acids obtained as a natural product.

Description: The present invention relates to a composition of a vinyl chloride-based resin (hereinafter referred to as a PVC) and more particularly to a PVC composition capable of giving a colourless moulded article emitting little offensive odour along with excellent mechanical properties, weatherability, heat stability, resistance against chemicals, and transparency, especially suitable as a moulding material for food containers. Shaped articles of PVC composition are in general inexpensive and have excellent mechanical properties, resistance against chemicals, weatherability, colourlessness and transparency and the flexibility or rigidity thereof can be freely controlled by compounding the PVC composition with a suitable amount of a plasticizer, so that they are employed in a wide field of applications including not only household commodities but also a variety of industrial materials. A defect in PVCs in general is that the resin is usually relatively poor in heat resistance, suffering discoloration at the temperature which the PVC composition encounters in the course of the moulding process unless the PVC composition is admixed with a substantial amount of a stabilizer. Various types of stabilizers are known and in practical use in the prior art, of which metal-containing organic compounds are typical ones. When the PVC composition is used as a moulding material for food containers, it is essential that the stabilizer be absolutely free from the problem of toxicity in addition to the requirement that it should not reduce the transparency of articles moulded from the PVC composition. Examples of stabilizers suitable for food containers are classified into three types, including octyl tin mercaptide compounds, octyl tin maleates and combinations of calcium soap, zinc soap and an auxiliary agent, e.g. epoxidated soybean oil and organic phosphite compounds. These three types of stabilizers have their own advantages and disadvantages. For example, the tin mercaptide compounds exhibit excellent performance as a stabilizer in respect of the transparency, low initial colouring and heat stability of shaped articles made from the PVC composition but they are not suitable for use in food containers because of the very unpleasant odour characteristic of mercaptans, although these compounds are most promising for use in food containers if it were not for the malodour. The tin maleate compounds are free from the problem of malodour and capable of giving moderate heat stability to the PVC composition but are disadvantageous due to the relatively high initial colouring and yellowing of the shaped articles moulded from PVC compositions containing the same. The metal soap-based stabilizers are defective in that they give insufficient improvement in the heat stability of the PVC composition, although they have no problems relative to the malodour and initial colouring of the shaped articles. Various attempts and proposals have been made to remedy the above-mentioned defects in the conventional stabilizers, for example by incorporating special substituent groups in the stabilizer compound or by the admixture of the PVC composition with a special additive but none of the attempts and proposals has been a complete solution of the problem. SUMMARY OF THE INVENTION The present invention accordingly has as an object to provide a novel PVC composition compounded with an organic tin mercaptide compound as a stabilizer but still free from the above-mentioned disadvantages caused by the use of a mercaptide compound, without decreasing the inherently excellent stabilizing effect exhibited by the organic tin mercaptide compound. The polyvinyl chloride resin-based composition of the invention comprises, as a blend: (a) a polyvinyl chloride resin; (b) a deodorizing agent selected from the group consisting of diterpenic acid compounds and rosins; and (c) an organic tin mercaptide compound, the total amount of the deodorizing agent and the organic tin mercaptide compound being in the range from 1 to 5 parts by weight per 100 parts by weight of the polyvinyl chloride resin and the weight ratio of the deodorizing agent to the organic tin mercaptide compound being in the range from 3:97 to 60:40. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As is described above, the most characteristic ingredient in the PVC composition according to the invention is the specific deodorizing agent which is a diterpenic acid compound or a rosin, which latter is a crude mixture of diterpenic acids obtained as a natural product. This deodorizing agent is specifically effective in deodorizing the PVC composition compounded with an organic tin mercaptide compound as a stabilizer to such an extent that the moulded articles derived from the PVC composition are substantially free from any malodour and are therefore suitable for food containers. The polyvinyl chloride resin as the component (a) of the PVC composition is not limited to homopolymeric PVC resins but can be a copolymeric PVC resin obtained by the copolymerization of a major amount of vinyl chloride momomer with a minor amount of one or more other momomers copolymerizable with vinyl chloride, exemplified by vinyl esters, e.g. vinyl acetate and vinyl propionate, acrylic and methacrylic esters, e.g. methyl acrylate, ethyl acrylate and methyl methacrylate, olefins, e.g. ethylene and propylene, maleic anhydride, acrylonitrile, styrene, vinylidene chloride. The PVC resin is prepared by any known process of polymerization including suspension polymerization, emulsion polymerization, bulk polymerization, solution polymerization. The diterpenic acid used in the invention is a compound expressed by the molecular formula C₁₉H₂₉COOH and the diterpenic acid compounds are exemplified by abietic acid, neoabietic acid, dihydroabietic acid, tetrahydroabietic acid, dehydroabietic acid, d -pimaric acid, iso- d -pimaric acid, levopimaric acid, podocarpic acid, agathene dicarboxylic acid and rubenic acid. The rosins as a natural product of a mixture of these diterpenic acid compounds include gum rosins, wood rosins and tall oil rosins. Abietic acid among the above-named ones is preferred in view of its availability, although the other compounds are equally effective. These diterpenic acid compounds and rosins can be used either singly or as a combination of two kinds or more according to need. The diterpenic acid compounds and rosins are obtained usually in the form of sandy granules or lumps colored light yellow or light brown and can be used as such or finely pulverized. When any trace colouring of the PVC composition due to compounding with these coloured agents should be avoided, it is recommended to purify the diterpenic acid compounds and rosins by recrystallization from a solution in an organic solvent such as ethyl alcohol and benzene to effect decolorization. The organic tin mercaptide compounds as the component(c) act as a stabilizer in the PVC composition. The organic tin mercaptide compounds include methyl tin mercaptides, butyl tin mercaptides, octyl tin mercaptides, of which octyl tin mercaptides are preferred in view of the low toxicity when the PVC composition is shaped into food containers. The amounts of the deodorizing agent and the organic tin mercaptide compound in the inventive PVC composition should be such that the total amount of the deodorizing agent and the organic tin mercaptide compound is in the range from 1 to 5 parts by weight per 100 parts by weight of the polyvinyl chloride resin and the weight ratio of the deodorizing agent to the organic tin mercaptide compound is in the range from 3:97 to 60:40 or, preferably, in the range from 5:95 to 50:50. When the amount of the organic tin mercaptide compound is too small, the desired heat-stabilizing effect cannot be obtained as a matter of course. When the amount of the organic tin mercaptide compound is too large on the other hand, the malodour due to the mercaptide may be emitted despite the formulation of the deodorizing agent. When the amount of the deodorizing agent is too small, the deodorizing effect can of course not be exhibited to a full extent. When the amount of the deodorizing agent is too large on the other hand, the PVC composition may have some stickiness so that the workability in moulding is greatly reduced in addition to the problem of relative decrease in the amount of the heat stabilizer. In this regard, the amount of the organic tin mercaptide compound should be at least 0.4 part by weight per 100 parts by weight of the PVC resin. The deodorizing agent and the organic tin mercaptide compound can be compounded with the PVC resin in any suitable manner either separately or as a blend prepared beforehand since they are compatible with each other when the organic tin mercaptide compound is a liquid. When the organic tin mercaptide compound is a solid, a powdery mixture thereof with the also powdery deodorizing agent retains free-flowability without causing any troubles in handling. In addition, both of them have good compatibility with the PVC resin so that the PVC composition compounded therewith never suffers from a decrease in transparency. Moreover, the PVC composition compounded with these materials is never imparted with stickiness, so that no difficulties are encountered in the compounding of the composition and in the moulding procedure. It is of course possible according to need to compound the PVC composition further with various kinds of known additives conventionally compounded in PVC compositions, including impact strength-improvers, lubricants, fillers, coloring agents, ultraviolet absorbers, antioxidants and the like, without reducing the heat-stabilizing and deodorizing effects. In the following, examples and comparative examples are given to illustrate the invention in more detail but by way of example only. Example 1 and Comparative Example 1. Nine PVC compositions, referred to as the compositions No. 1 to No. 9 hereinbelow, were prepared each from 100 g of a polyvinyl chloride resin (TK-700, a product of Shin-Etsu Chemical Co.), 15 g of an MBS resin (Metablen C-202, a product of Mitsubishi Rayon Co.), 1 g of glycerin monostearate (Rikemal S-100, a product of Riken Vitamin Co.), 2 g of an organic tin mercaptide (TVS No. 8831, a product of Nitto Kasei Co., referred to as the mercaptide hereinbelow) and a deodorizing agent specified below, first by blending in a beaker and then by milling on a 152.4 mm (6-inch) roller mill having a surface temperature of 170°C for 5 minutes. The thus-compounded PVC compositions were each shaped into a sheet having a thickness of 0.8 mm. The deodorizing agent compounded in each of the PVC compositions No. 1 to No. 9 and the amount thereof were: 0.1 g of abietic acid as purchased in the composition No. 1; 0.2 g of abietic acid as purchased in the composition No. 2; 0.5 g of abietic acid as purchased in the composition No. 3; 1.0 g of abietic acid as purchased in the composition No. 4; 1.0 g of refined abietic acid in the composition No. 5; 0.2 g of refined abietic acid in the composition No. 6; 0.2 g of rosin in the composition No. 7; 0.5 g of rosin in the composition No. 8; and a combination of 0.1 g of abietic acid as purchased and 0.1 g of rosin in the composition No. 9. The abietic acid used above was a light yellow product supplied by Seiken Kagaku Co. and the refined abietic acid was white and prepared by recrystallizing the above-mentioned product as purchased from methyl alcohol. The rosin was supplied by Arakawa Chemical Co. For comparison, three more PVC compositions, referred to as the compositions No. 10 to No. 12 hereinbelow, were prepared each with the same formulation as in the composition No. 1 excepting omission of the abietic acid in the composition No. 10, replacement of 2.0 g of the mercaptide with 2.0 of octyl tin maleate (TBS No. 8813, a product of Nitto Kasei Co., referred to as the maleate hereinbelow) and omission of the abietic acid in the composition No. 11, and replacement of 2.0 g of the mercaptide with 5 g of a calcium-zinc soap-based stabilizer, referred to as the Ca-Zn hereinbelow (a combination of 2 g of MARK SP and 3 g of ADK CIZER 0130P, each a product of Adeka Argus Kagaku Co.) and omission of the abietic acid in the composition No. 12. These comparative compositions were each shaped into a sheet of 0.8mm thickness. Each of the sheets prepared above was subjected to the evaluation tests for the following items by the method described below. I. Heat stability Test pieces of the sheet were heated in a Geer's oven at 190°C and taken out one by one every 15 minutes to be examined visually and rated in 10 ratings for coloration up to 90 minutes. The results are shown in Table 1 below. The ratings of point 1 to point 10 approximately correspond to the yellowness YI and colour difference ΔE tabulated below. II. Malodour The sheet was chopped into square pieces of 3 to 4 mm a side and 10 g thereof were taken in a narrow-mouth glass bottle of 50 ml capacity together with 10 ml of pure water. The bottle hermetically sealed with a septum of Teflon-butyl rubber was heated at 80°C for 24 hours. Thereafter, the septum was removed and the smell at the bottle mouth was smelled immediately by five panel members who were requested to evaluate the smell in 6 ratings of point 0 to point 5, point 0 corresponding to pure water and point 5 corresponding to the composition No. 10. The results are shown in Table 2. III. Initial coloration (yellowness YI) Measurement was made according to the method specified in JIS K 7105, 6.3. The results are shown in Table 2. IV. Transparency (haze) Measurement was made according to the method specified in JIS K 7105, 6.4. The results are shown in Table 2. Example 2 and Comparative Example 2. Seven PVC compositions according to the invention, referred to as the compositions No. 13 to No. 19 hereinbelow, and three comparative PVC compositions, referred to as the compositions No. 20 to No. 22 hereinbelow, were prepared each in the same manner and in the same formulation as the composition No. 1 excepting a change of the amount of the mercaptide or replacement of the mercaptide with or addition of another stabilizer shown in Table 3 below and change of the amount or omission of the abietic acid as purchased or replacement with or addition of another deodorizing agent as shown in the same table. The amount of the additives in Table 3 is given in g. These PVC compositions were each shaped into a sheet and subjected to the evaluation tests in the same manner as in the preceding examples. The results of the heat stability test are shown in Table 4 below and the results of the other tests are shown in Table 5 below.

Claims: A polyvinyl chloride resin-based composition which comprises, as a blend: (a) a polyvinyl chloride resin; (b) a deodorizing agent selected from the group consisting of diterpenic acid compounds and rosins; and (c) an organic tin mercaptide compound, the total amount of the deodorizing agent and the organic tin mercaptide compound being in the range from 1 to 5 parts by weight per 100 parts by weight of the polyvinyl chloride resin and the weight ratio of the deodorizing agent to the organic tin mercaptide compound being in the range from 3:97 to 60:40. A polyvinyl chloride resin-based composition as claimed in claim 1, wherein the diterpenic acid compound is abietic acid. A polyvinyl chloride resin-based composition as claimed in claim 1 or claim 2, wherein the weight ratio of the deodorizing agent to the organic tin mercaptide compound is in the range from 5:95 to 50:50. A polyvinyl chloride resin-based composition as claimed in any of claims 1 to 3, wherein the organic tin mercaptide compound is octyl tin mercaptide.

Inventors: MATSUMOTO, OSAMU, TSUCHIDA, MICHINORI
Applicants: SHIN-ETSU CHEMICAL CO., LTD.
Application year: 1990
Main classification: C08K5
IPC codes: C08L27, C08K5