Thermoplastic Resin Composition

This invention relates to a thermoplastic resin composition and, more particularly, to a thermoplastic resin composition prepared by adding a plasticizer having sufficient sanitary safety to a vinyl chloride resin.

In recent years, owing to the sanitary problems, there is a tendency toward avoiding the use of phthalate plasticizers and 2-ethylhexanol plasticizers in vinyl chloride resin products to which sanitary safety is indispensable. In such a field, the development of novel plasticizers which are sufficiently safe and satisfactory with respect to economy and function has been demanded.

As a result of an eager study made to meet such a demand, we have found that a glycerin ester having acyl groups comprising those having 10 to 14 carbon atoms and those having 2 carbon atoms is excellent as a plasticizer for vinyl chloride resins, while glycerin esters having acyl groups comprising those having 18 carbon atoms and those having 2 carbon atoms, known conventionally in the art, have poor plasticizing ability, and achieved this invention.

The glycerin ester of this invention is accepted at present also as a food additive, can therefore be used in the vinyl chloride resin without any problem and, because the ester itself is edible, can meet demands of related industries and consumers.

Because of its nontoxicity and edibility, the glycerin ester plasticizer of this invention can be used as a plasticizer not only for packaging materials in direct contact with food, that is, packaging films, wraps and molded containers, but also for vinyl chloride resin products required to have sanitary safety, such as medical appliances, tubes and toys.

The glycerin ester of this invention is represented by the following general formula ##STR2## wherein R.sub.1, R.sub.2 and R.sub.3 represent each an acyl group or a hydrogen atom and said acyl group comprises one having 2 carbon atoms (hereinafter referred to as C.sub.2 acyl group) and one consisting mainly of those having 10 to 14 carbon atoms (hereinafter referred to as C.sub.10-14 acyl group), the C.sub.2 acyl group is present in an amount, on the average, of up to 2 mol per mol of glycerin, the C.sub.10-14 acyl group is present in an amount, on the average, of at least 0.9 mol per mol of glycerin and the total amount of the C.sub.2 acyl and C.sub.10-14 acyl groups is, on the average, in the range of 2.7 to 3.0 mol per mol of glycerin. The total amount of the acyl groups is preferably in the range of 2.9 to 3.0 mol per mol of glycerin.

The C.sub.2 acyl group can be derived from acetic acid and, in practice, there can be used general industrial acetic acid, edible acetic acid, acetic anhydride and glycerin triacetate.

The C.sub.10-14 acyl group can generally be derived from coconut fatty acids, hardened coconut fatty acids, synthetic fatty acid, fatty acid from fractionated and purified natural oil and fat but because of function, economy, availability and the like, coconut fatty acids or hardened coconut fatty acids is preferred. These fatty acids contain 12-carbon acids as the main components.

Moreover, in view of the purpose of a plasticizer in itself, the highest possible content of the C.sub.10-14 acyl groups is preferred, that is, when the content of 10-carbon or lower fatty acids is increased, the plasticizing ability increases but the volatility also increases unfavorably, causing troubles during molding or an increased extractability of moldings. On the contrary, an increase in the content of 14-carbon or higher components causes a decrease in plasticizing ability and gives rise to a problem in transparency and bleeding.

Thus, from the viewpoint of function and economy, the content of 10- to 14-carbon components in the C.sub.10-14 acyl group is preferably at least 50% and the higher, the better.

Ideally, the proportion among glycerin, C.sub.2 acyl group and C.sub.10-14 acyl group is 1:2:1 (mol ratio) but, in practice, it is almost impossible to produce such a product industrially. An increase of the C.sub.2 acyl group relative to glycerin leads to an increase of volatile components, while an increase of the C.sub.10-14 acyl group leads to a decrease in plasticizing ability. Therefore, the content of the C.sub.2 acyl group is, on the average, up to 2 mol, preferably, 2 mol per mol of glycerin and the content of the C.sub.10-14 acyl group is, on the average, at least 0.9 mol or preferably 1 mol per mol of glycerin. Since the total amount of the acyl groups is, on the average, 2.7 to 3.0 mol per mol of glycerin, the balance consists of hydrogen atoms.

It is preferred that the glycerin ester used in this invention has a hydroxyl value of 50 or less, most suitably, 30 or less.

Similarly, it is preferred that the glycerin ester has a Reichert-Meissl value of at least 151, most suitably, at least 170. Neither case of a hydroxyl value of more than 50 nor case of a Reichert-Meissl value of less than 151 is preferred because such conditions cause a decrease in the plasticizing ability and an adverse effect on the bleeding and transparency.

The glycerin ester of this invention can usually be manufactured by purifying a product obtained by the interesterification of oil or fat with glycerin triacetate or by the direct acetylation of a fatty acid monoglyceride with acetic anhydride.

The glycerin ester of this invention can be added as a plasticizer in an amount of 1 to 100 parts by weight per 100 parts by weight of a vinyl chloride resin.

By the term "vinyl chloride resin" used herein is meant a vinyl chloride polymer or a vinyl chloride copolymer such as vinyl chloride/vinyl acetate copolymer, vinyl chloride/vinylidene chloride copolymer, vinyl chloride/ethylene copolymer or a copolymer prepared by grafting vinyl chloride onto ethylene/vinyl acetate copolymer. The thermoplastic resin composition of this invention can also include a polymer blend of the above-mentioned vinyl chloride polymer or vinyl chloride copolymer and an olefin polymer which is a methacryl polymer or acrylonitrile-butadiene-styrene polymer (ABS resin).

This invention will be described below with reference to examples, but it should be noted that the invention is not limited by these examples.

In the examples, the samples as set forth below and di-octyl adipate (DOA) and di-octyl phthalate (DOP) taken as comparative samples were used.

Each sample was tested for its fundamental functions as a plasticizer by using the following formulation.

PVC (P=1,050), Zeon 103 EP--100 parts by weight

Ca-Zn stabilizer--1

epoxidized soybean oil--3

plasticizer--50

A predetermined amount of each sample was added to the above formulation and the mixture was kneaded at 150.degree. to 155.degree. C. for 5 minutes between 8-inch test rollers. The rolled sheet was further pressed at 160.degree. C. and 150 kg/cm.sup.2 by using a compression molding machine to form a 1-mm thick sheet.

The results show that the plasticizers of this invention have values similar to those of DOP and DOA, whereas the comparative plasticizers X, Y and Z have inferior values, which indicate that the comparative plasticizers X, Y and Z have insufficient function as plasticizers.

The plasticizers of this invention can be considered to have plasticizing abilities comparable to that of DOP.

Evaluation of Function by using a PVC paste resin formulation.

PVC (P=1,300) Kaneka PSM-31--100 parts by weight

Ca-Zn liquid stabilizer--3

plasticizer--60

A compound after dearation was spread over a glass plate to form a 1-mm thick film, the film was allowed to gel for 15 minutes in a Gear oven at 180.degree. C., the resulting sheet was left to stand at room temperature for a week, the bled matter was washed off with an acetone/IPA mixture. The sheet was dried to measure its weight loss.

The results show that the comparative plasticizers X, Y and Z are not satisfactory but the plasticizers of this invention show values superior to that of DOA though they are inferior to that of DOP.

Evaluation by using an ethylene/vinyl chloride copolymer sheet formulation.

ethylene/vinyl copolymer 1 (P=650)--50 parts by weight

ethylene/vinyl copolymer 2 (P=800)--50

Ca-Zn stabilizer--2.0

methylmethacryl-butadiene-styrene resin--5.0

lubricant, stearic acid monoglyceride--1.0

polyethylene wax--0.3

plasticizer--3.0

The above formulation was kneaded at 180.degree.-190.degree. C. for 5 minutes between 8-inch test rollers. The processability was judged at this point. Next, the rolled sheet was further pressed at 180.degree. C. and 100 kg/cm.sup.2 to form a 1-mm thick sheet, and then the transparency was measured.

The results show that the plasticizers of this invention have functions comparable to those of DOA and DOP.

Evaluation by using a PVC wrap formulation.

PVC (P=1,050)--100 parts by weight

epoxidized soybean oil--10

Ca-Zn stabilizer--2

chelator--0.5

antifogging agent sorbitan laurate--1.0

polyoxyethylene alkyl ether--1.0

plasticizer--35

The above formulation was molded into a wrap film by use of a 40-mm extruder and the film was subjected to tests for evaluation of properties.

made by Tanabe Plastics Machine Co., Ltd.

screw diameter 40 mm, L/D=24, die 400 mm wide T-die,

coathunger type

cylinder head temperature--195.degree. C.

T-die temperature--205.degree. C.

screw speed--25 rpm

take-off speed--20 m/min

The results show that as compared with the comparative plasticizers X, Y and Z, the plasticizers of this invention are excellent in any of processability, transparency, bleeding and antifogging property and have performances comparable to that of DOA.