GB2052525A

GB2052525A - Method for the preparation of shaped articles of vinyl chloride based resin with improved surface properties

Info

Publication number: GB2052525A
Application number: GB8019571A
Authority: GB
Original assignee: Shin Etsu Chemical Co Ltd
Current assignee: Shin Etsu Chemical Co Ltd
Priority date: 1979-06-26
Filing date: 1980-06-16
Publication date: 1981-01-28
Also published as: FR2459813A1; GB2052525B; DE3023176A1; FR2459813B1

Abstract

A method for preventing bleeding of a plasticizer or other additive ingredients on the surface of from a vinyl chloride-based resin article comprises blending the vinyl chloride resin prior to fabrication into shaped articles, with 0.5 to 50% by weight of a crosslinking aid selected from allyl group-containing compounds, e.g. triallyl cyanurate and triallyl isocyanurate, and esters of methacrylic acid, e.g. diethyleneglycol dimethacrylate and trimethylolpropane trimethacrylate and then fabricating into a shaped article, which is then exposed to low temperature plasma of a gas having no polymerizability in the plasma condition, e.g. carbon monoxide, so that a barrier layer with a controlled degree of crosslinking is formed in the surface. The effect is very durable over a long period of time so that plasticizer bleeding is effectively prevented even after prolonged outdoor use or weathering.

Description

SPECIFICATION Method for the preparation of shaped articles of vinyl chloride based resin with improved surface properties The present invention relates to a method for the preparation of a shaped article of a vinyl chloride-based resin with improved surface properties, more particularly, a method for the preparation of a shaped article of a vinyl chloride-based resin in which bleeding or blooming of the plasticizer and other additive ingredients formulated therein on the surface is substantially reduced.

Needless to say, vinyl chloride-based resins are one of the most important thermoplastic resins, owing to their excellent and very versatile properties and their relative inexpensiveness, such that they are widely employed in a variety of application fields having been shaped into various articles. In particular, rigidity or flexibility of shaped articles of vinyl chloride-based resins can be adequately controlled by formulating the resin with a plasticizer. The thus plasticized resins can give relatively flexible shaped articles so that plasticized resin compositions are fabricated into films, sheets, synthetic leathers, tubes, hoses, bags, coating materials and the like used in various fields such as medical instruments, packaging materials for foodstuffs, materials for agricultural use, building materials and the like.

Furthermore, it is a very common practice for vinyl chloride-based resins to be formulated with various kinds of additive ingredients such as flame retardants, anti-oxidants, ultraviolet absorbers, lubricants and others according to the need for improvement in the workability of the resin composition and in the properties of the articles shaped from the resin composition.

One of the most serious problems with the articles shaped from the vinyl chloride-based resin composition formulated with the additive ingredients, typically, a plasticizer, is that the plasticizer contained in the shaped article may sometimes migrate toward the surface of the article and exude on the surface of the article in the long run resuiting in inferior properties of the plasticized vinyl chloridebased resin articles. This phenomenon is usually called "bleeding", prevention of which is one of the most important and difficult problems in the technology of synthetic resin processing.

Bleeding of the plasticizer is undesirable not only due to the deterioration of the properties of the shaped articles but also due to the transfer of the plasticizer exuded on the surface of the article to the surface of any other body in contact with the shaped article of the plasticized vinyl chloride-based resin composition. Along with the loss in the attractiveness of the surface appearance of the articles, bleeding or transfer of the plasticizer is especially undesirable when the shaped article is used in a medical tool or instrument or in contact with foods because physiological inertness of plasticizers to the human body has not been established (in general) so that the use of plasticized vinyl chloride-based resin compositions in these fields is greatly limited. Similar problems are involved in the use of shaped articles containing the other additive ingredients.

Various attempts have been made to solve the above described problem of surface bleeding of plasticizers and the like. The methods hitherto proposed for the purpose include a method of treatment or irradiation of the surface of the article with ionizing radiation, electron beams or ultraviolet light as well as with high voltage, high frequency electric corona discharge and a method of chemical treatment.

These methods are to some extent effective to improve heat resistance and anti-solvent resistance and to impart affinity for water, anti-static properties and printability to the surface but relatively ineffective in preventing the bleeding of plasticizers and the like with, instead, adverse effects on the useful properties inherently possessed by the vinyl chloride-based resins.

For example, irradiation with ionizing radiation or high energy electron beams may produce crosslinking between the polymer molecules not only in the superficial layer of the shaped article but also in the subsurface layer due to the excessively high energy of the radiation so that the flexibility which is the most characteristic feature of the plasticized vinyl chloride resin articles is largely lost.

Treatment with ultra-violet light is undesirable because of coloring of the surface due to the degradation of the polymer molecules in the surface layer of the shaped article. The chemical method is not free from the problems of surface erosion of the shaped articles and poor adhesion or durability of the films provided on the surface of the article by the chemical means. Thus, no reliable and effective methods have been developed for preventing surface bleeding of the plasticizers or other additive ingredients on the surface of the shaped articles of vinyl chloride-based resin compositions.

The method of the present invention established as a result of the extensive investigations undertaken by the inventors is based on the discovery that, when an article shaped from a vinyl chloride-based resin composition containing a specified amount of a crosslinking aid selected from esters of methacrylic acid and allyl group-containing compounds is subjected to exposure to low temperature plasma, a barrier layer effective for preventing bleeding of the plasticizer is efficiently formed on the surface by the crosslink formation between the polymer molecules, the crosslink formation being accelerated by the crosslinking aid formulated therein. Furthermore, the plasticizer bleeding prevention effect obtained is durable over a long period of storage or use in contrast to the cases of mere plasma treatment without the addition of the crosslinking aid.

The method of the present invention for the preparation of a shaped article of a vinyl chloridebased resin with improved or modified surface properties comprises the steps of (a) blending 100 parts by weight of a vinyl chloride-based resin with from 0.5 to 50 parts by weight of a crosslinking aid selected from allyl group-containing compounds and esters of methacrylic acid to form a resin composition, (b) fabricating a shaped article from the resin composition, and (c) subjecting the surface of the shaped article to exposure to low temperature plasma of a gas having no polymerizability in the plasma condition, under a pressure of from 0.001 Torr to 10 Torr.

Preferred forms of the invention will now be described.

The base component of the shaped article to be manufactured by the method of the invention is a vinyl chloride-based resin which may be not only a homopolymeric vinyl chloride resin but also various kinds of copolymeric resins of vinyl chloride, of which the main component, say 50% by weight or more, is vinyl chloride; the vinyl chloride may be copolymerised with one or more of copolymerizable monomers exemplified by vinyl esters such as vinyl acetate, vinyl ethers such as vinyl ethyl ether, acrylic acid and esters thereof, methacrylic acid and esters thereof, maleic acid and esters and anhydride thereof, fumaric acid and esters thereof, aromatic vinyl compounds such as styrene, vinylidene halides such as vinylidene chloride, acrylonitrile, methacrylonitrile and olefins such as ethylene, propylene and the like.

The crosslinking aid, which is used as an essential ingredient in the composition for the shaped articles, is a compound selected from allyl group-containing compounds and esters of methacrylic acid.

The allyl group-containing compounds are exemplified by allyl alcohol, diallyl ether, diallyl phthalate, diallyl fumarate, tetraallyl oxyethane, triallyl cyanurate, triallyl isocyanurate and the like, among which those compounds having at least two allyl groups in the molecule are preferred.

The esters of methacrylic acid are exemplified by methyl methacrylate, lauryl methacrylate, ethyleneglycol dimethacrylate, triethyleneglycol dimethacrylate, tetraethyleneglycol dimethacrylate, polyethyleneglycol dimethacrylate, trimethylolpropane trimethacrylate and the like, among which dimethacrylates and trimethacrylates are preferred to the monoesters.

The above specified crosslinking aid is formulated with the vinyl chloride-based resin in an amount from 0.5 to 50 parts by weight per 100 parts by weight of the resin. When the amount of the crosslinking aid is too small, the desired effects can naturally not be obtained while an excessively large amount of the crosslinking aid is undesirable due to the deterioration of the advantageous properties inherent in the vinyl chloride-based resins with, instead, bleeding of the crosslinking aid per se on the surface of the shaped articles.

To achieve the main purpose of the invention, the shaped articles of the vinyl chloride-based resin to be manufactured by the method of the invention should contain at least one kind of additive ingredient other than the above mentioned crosslinking aids.

For example, plasticizers are formulated in the resin composition when flexibility or reduced hardness is desired for the shaped article as exemplified by esters of phthalic acid such as dioctyl phthalate, butylbenzyl phthalate and the like, esters of aliphatic dibasic acids such as dioctyl adipate, dibutyl sebacate and the like, glycol esters such as esters of pentaerithritol, diethyleneglycol dibenzoate and the like, esters of fatty acids such as methyl acetylricinolate and the like, esters of phosphoric acid such as tricresyl phosphate, triphenyl phosphate and the like, epoxidated oils such as epoxidated soybean oil, epoxidated linseed oil and the like, esters of citric acid such as acetyl tributyl citrate, acetyl trioctyl citrate and the like, trialkyl trimellitate, tetra-n-octyl pyromellitate and polypropylene adipate as well as polyesters and plasticizers having diverse chemical structures.

Other kinds of additive ingredients for improving the properties of the composition such as heat resistance, lubricity, stability and the like include stabilizers such as metal salts of carboxylic acids, e.g.

calcium stearate, barium stearate and cadmium stearate, lead compounds, e.g. tribasic lead sulfate and dibasic lead phosphite and organotin compounds, e.g. dibutyltin dilaurate, di-n-octyltin maleate and din-octyltin mercaptide; lubricants such as higher fatty acids and esters thereof, e.g. butyl stearate, fatty acid am ides, e.g. ethylene bisstearoamide, and polyethylene waxes; and other kinds of additive ingredients conventionally used for formulating vinyl chloride-based resin compositions for shaping articles including fillers, ultraviolet absorbers, antistatic agents, anti-fogging agents, pigments and dyes.

The vinyl chloride-based resin used in the method of the invention may be a polymer blend, in particular, a blend with a polymer rubbery elastomer such as a copolymer of ethylene and vinyl acetate, a copolymer of acrylonitrile and butadiene, a copolymer of styrene and acrylonitrile, a copolymer of methyl methacrylate, styrene and butadiene, a copolymer of acrylonitrile, styrene and butadiene, a polyamide resin, a polymer of caprnlactam, an epoxy-modified polybutadiene resin and a polyurethane elastomer, although in a limited amount not exceeding 50 parts by weight per 100 parts by weight of the vinyl chloride-based resin.

The vinyl chloride-based resin composition obtained by blending the above described ingredients is then fabricated into shaped articles. The method for shaping the resin composition into articles may be a conventional one such as extrusion molding, injection molding, calendering, inflation and compression molding according to the desired shape of the article. The shapes of the articles are not particularly significant provided that the subsequent treatment with low temperature plasma can be effected uniformly over the surface of the shaped article.

The next step is the exposure of the surface of the shaped article to low temperature plasma of a gas having no polymerizability in the plasma condition under a pressure in the range from 0.001 Torr to 10 Torr. The low temperature plasma is readily generated in the gaseous atmosphere of the above specified pressure by applying a high frequency, e.g. 13.56 MHz, electric power of 10 to 500 watts to electrodes so effecting electric discharge through the atmosphere. Satisfactory results can be obtained either by electrode discharge or by electrodeless discharge. The optimum time for the plasma treatment may differ widely depending on the energy density of the plasma atmosphere but it is usually in the range from a few seconds to several tens of minutes.

The frequency band for the electric discharge is not limited to the above mentioned high frequency region but may range from direct current to low frequency to microwave regions. The mode of the electric discharge is also not important and includes, in addition to glow discharge, spark discharge and silent discharge. Exterior electrodes and inside electrodes as well as a coiled electrode may be used as the discharge electrode and they may be connected to the power supply by capacitive coupling or inductive coupling. At any rate, however, it is a requirement that the surface of the shaped article is not subject to thermal denaturation by the heat evolved in the electric discharge.

What is meant by the term "a gas having no polymerizability in the plasma condition" is a gas from which products with high molecular weights are not formed when low temperature plasma is generated in a low pressure atmosphere of the gas. Suitable gases are mostly inorganic gases exemplified by helium, neon, argon, nitrogen, nitrous oxide, nitrogen dioxide, oxygen, air, carbon monoxide, carbon dioxide, hydrogen, chlorine and hydrogen chloride. These gases are used either singly or as a mixture of two kinds or more. The pressure of the gaseous atmosphere in the plasma generating chamber is in the range from 0.001 Torrto 10 Torr, preferably from 0.01 Torrto 1 Torr, in order to obtain stable plasma discharge.

When the shaped article of the vinyl chloride-based resin composition is subjected to exposure to the low temperature plasma in the conditions as described above, a barrier layer, which is effective in preventing bleeding of the plasticizer and other additive ingredients on the surface of the shaped articles, is formed on the surface with high efficiency. The thus formed barrier layer has an adequately controlled crosslinking density so as to possess sufficient flexibility or pliability so as not to adversely affect the usefulness of the shaped articles. In particular, the effects of the method of the invention are very durable even under weathering conditions so that the effectiveness of the method is not lost even after prolonged outdoor use of the shaped article.Furthermore, shaped articles plasma-treated in accordance with method have surface properties such as increased affinity for water, low susceptibility to stain, improved anti-oil and anti-chemicals resistance and the like.

Following are Examples to illustrate the method of the present invention in further detail but not to limit the scope of the invention. In the following Examples, the effectiveness of the method, i.e.

decreased amounts of plasticizer bleeding on the surface of the shaped articles, was evaluated by the procedure described below. Thus, a piece of a sheet of the test specimen was placed on the bottom of a cylindrical extraction vessel of 100 ml capacity to expose 26 cm2 area of the plasma-treated surface and brought into contact with 50 ml of n-hexane introduced into the vessel followed by shaking for 2 hours at 370C with subsequent gas chromatographic analysis of the n-hexane extract to determine the amount of the plasticizer extracted from the test piece into the solvent. In the following Examples, the plasticizer bleeding was determined directly after the plasma treatment as well as after accelerated weathering of 100 hours or 500 hours in a weathering accelerator manufactured by Toyo Rika Co., Model WESUN HC.In some of the Examples, actual outdoor exposure was undertaken for 3 to 12 months in place of the accelerated weathering test as above.

EXAMPLE 1 Resin compositions were prepared each by blending 1 00 parts by weight of a homopolymeric vinyl chloride resin (TK-1 300, a product name of Shin-Etsu Chemical Co., Japan), 50 parts by weight of dioctyl phthalate, 1.5 parts by weight of calcium stearate and 1.5 parts by weight of zinc stearate without or with addition of 5 parts by weight of triallyl cyanurate and kneading of the blend in a roller mill at 1 600C for 10 minutes. Each of the resin compositions was fabricated by compression molding at 1 650C into sheets of 0.5 mm thickness.

The sheet thus prepared was placed in a plasma generating chamber where the surface of the sheet was exposed to low temperature plasma generated by the discharge with application of high frequency electric power of 1 50 watts at 13.56 MHz for 10 minutes while the atmosphere in the chamber was controlled and kept at 0.4 Torr by passing carbon monoxide gas under a reduced pressure.

The amount of plasticizer (dioctyl phthalate) bleeding on the surface of each of the sheet samples was determined by the procedure described above as prepared or directly after plasma treatment as well as after accelerated weathering for 100 hours or 500 hours to give the results in mg as set out in Table 1 below.

TABLE 1 (amount of extraction, mg)

Sample No. 1 2 3 4 Triallyl cyanurate No No Yes Yes Plasma-treatment No Yes No Yes Initial value 156 1.04 148 0.52 After accelerated 100 hours - 130 - 0.52 weathering of 500 hours - 143 - 1.04 EXAMPLE 2 The formulation and the fabrication procedure of sheet samples were just the same as in the preceding Example except that 5 parts by weight of triallyl cyanurate were replaced with 10 parts by weight of triallyl isocyanurate per 100 parts by weight of the vinyl chloride resin when it was added.

The plasma treatment of the sample sheets was carried out in the same plasma generating chamber as in Example 1 in which the high frequency electric power was increased to 300 watts and the time of the treatment was shortened to 5 minutes. The gas filling the chamber was a 10:90 by volume gaseous mixture of carbon monoxide and argon under a pressure of 0.8 Torr. The extraction test with n-hexane was undertaken for each of the sample sheets to give the results in mg set out in Table 2 below.

TABLE 2 (amount of extraction, mg)

Sample No. 5 6 7 8 Triallyl isocyanurate No No Yes Yes Plasma-treatment C No Yes No Yes Initial value 1.30 143 0.78 After accelerated 100 hours ~ 130 ~ 1.30 weathering of 500 hours ~ of 1 2.08 EXAMPLE 3 The formulation and the fabrication procedure of sheet samples were just the same as in Example 2 except that triallyl isocyanurate was replaced with the same amount of triallyl cyanurate. The plasma treatment of the sheet samples was undertaken in the same plasma generating chamber as in the preceding Examples for 5 minutes but the electric power was further increased to 500 watts and the chamber was filled with carbon monoxide gas under a pressure of 0.1 5 Torr.

The extraction test with n-hexane was undertaken with the sheet samples as prepared or as plasma-treated as well as after 3 to 1 2 months of outdoor exposure to give the results set out in Table 3 below.

TABLE 3 (amount of extraction, mg)

Sample No. 9 10 11 12 Triallyl cyanurate No No Yes Yes Plasma-treatment No Yes No Yes Initial value 156 1.04 143 0.52 After outdoor 3 months - 78 - 0.78 exposure of 6 months - 143 - 0.78 12 months - - - 1.30 EXAMPLE 4 The formulation and the fabrication procedure of the sheet samples were just the same as in Example 3 except that triallyl cyanurate was replaced with the same amount of diethyleneglycol dimethacrylate. The conditions of the plasma-treatment were just the same as in Example 1. The results of the plasticizer extraction test with n-hexane undertaken with the sheet samples as prepared or as plasma-treated as well as after 100 hours or 500 hours of accelerated weathering were as set out in Table 4 below.

TABLE 4 (amount of extraction, mg)

Sample No. 13 14 15 16 Diethyleneglycol di- No No Yes Yes methacrylate Plasma-treatment No Yes No Yes Initial value 156 1.04 143 0.78 After accelerated 100 hours ~ 130 ~ 3.9 weathering of 500 hours - 143 - 13.0 EXAMPLE 5 The formulation and the fabrication procedure were the same as in Example 4 above except that diethyleneglycol dimethacrylate was replaced with the same amount of trimethylolpropane trimethacrylate.The conditions of the plasma-treatment of the sheet samples were just the same as in Example 2. The results of the plasticizer extraction test with n-hexane undertaken with the sheet samples as prepared or as plasma-treated as well as after accelerated weathering of 100 hours or 500 hours were as set out in Table 5 below.

TABLE 5 (amount of extraction, mg)

Sample No. I 17 18 19 20 Trimethylolpropane No No Yes Yes trimethacrylate Plasma-treatment No Yes No Yes Initial value 156 1.30 143 0.78 After accelerated 100 hours - 130 - 1.56 weathering of 500 hours - - - 5.2 EXAMPLE 6 The formulation and the fabrication procedure of the sheet samples as well as the conditions of the plasma-treatment were just the same as in Example 3 above except that 10 parts by weight of triallyl cyanurate were replaced with 15 parts by weight of diethyleneglycol dimethacrylate.

The results of the plasticizer extraction test with n-hexane undertaken with the sample sheets as prepared or as plasma-treated as well as after outdoor exposure of 3 to 12 months were as set out in Table 6 below.

TABLE 6 (amount of extraction, mg)

Sample No. | 21 | 22 3 23 1 24 Diethyleneglycol No No Yes Yes dimethacrylate Plasma treatment No Yes - No Yes Initial value 156 1.04 138 0.78 After outdoor 3 months - 78 - 1.30 exposure of 6 months - 143 3.12 12 months - - - 5.2

Claims

1. A method for the preparation of a shaped article of a-vinyl chloride-based resin with good surface properties which comprises (a) blending 100 parts by weight of a vinyl chloride-based resin with from 0.5 to 50 parts by weight of a crosslinking aid selected from allyl group-containing compounds and esters of methacrylic acid to form a resin composition, (b) fabricating a shaped article from the resin composition, and (c) subjecting the surface of the shaped article to exposure to low temperature plasma of a gas having no polymerizability in the plasma condition, under a pressure between 0.001 Torr and 10 Torr.

2. The method as claimed in claim 1 wherein the allyl group-containing compound has at least two allyl groups in the molecule.

3. The method as claimed in claim 2 wherein the allyl group-containing compound is triallyl cyanurate or triallyl isocyanurate.

4. The method as claimed in claim 1 wherein the ester of methacrylic acid is a diester or a triester of methacrylic acid.

5. The method as claimed in claim 4 wherein the diester of rnethacrylic acid is diethyleneglycol dimethacrylate.

6. The method as claimed in claim 4 wherein the triester of methacrylic acid is trimethylolpropane trimethacrylate.

7. An article shaped from a vinyl chloride-based resin composition comprising from 0.5 to 50 parts by weight of a crosslinking aid selected from allyl group-containing compounds and esters of methacrylic acid per 100 parts by weight of the vinyl chloride-based resin, the surface of said article having been exposed to low temperature plasma of a gas having no polymerizability in the plasma condition.

8. The method as claimed in claim 1 substantially as described in any of the Examples.

9. A shaped article prepared a method as claimed in any one of claims 1 to 6.