GB2048280A

GB2048280A - Method for preventing surface bleeding in polyvinyl chloride shaped articles

Info

Publication number: GB2048280A
Application number: GB8013649A
Authority: GB
Original assignee: Agency of Industrial Science and Technology; Shin Etsu Chemical Co Ltd
Current assignee: Shin Etsu Chemical Co Ltd; National Institute of Advanced Industrial Science and Technology AIST
Priority date: 1979-04-27
Filing date: 1980-04-25
Publication date: 1980-12-10
Also published as: JPS55144034A; DE3016048A1; FR2455065A1; FR2455065B1; GB2048280B; JPS5761776B2; DE3016048C2

Abstract

The invention provides a means for preventing bleeding of a plasticizer, e.g. di(2-ethylhexyl) phthalate, contained in a shaped article made of a plasticized vinyl chloride-based resin on to the surface of the shaped article. The surface of the shaped article containing the plasticizer is irradiated with ultraviolet light having an energy distribution predominantly in a wavelength range of from 105 to 200 nm in an atmosphere of oxygen or an oxygen-containing gaseous mixture of which the pressure of oxygen or the partial pressure of oxygen is in the range from 0.05 to 50 Torr.

Description

SPECIFICATION Method for preventing surface bleeding in polyvinyl chloride shaped articles The present invention relates to a method for preventing surface bleeding in shaped articles made of a polyvinyl chloride resin and, more particularly, to a method in which the surface of a shaped article of a polyvinyl chloride-based resin is subjected to chemical modification so as that migration and bleeding of a plasticizer or other additive ingredients formulated in the shaped article on to the surface of the shaped article in the lapse of time is substantially prevented or the plasticizer or other additive ingredients thus exuded on the surface of the article are prevented from transfer to the surface of another body being used in contact with the shaped article of polyvinyl chloride resin.

Needless to say, vinyl chloride-based resins belong to one of the most inexpensive classes of synthetic resins so that they are used extensively in a large quantity as a resin material for fabricating a variety of shaped articles such as films, sheets, plates and tubes as well as shaped articles of complicated or irregular forms to be used in very diversified fields of applications.

Vinyl chloride-based resins are, however, rarely fabricated into shaped articles as such but it is very common that a vinyl chloride-based resin is fabricated in a formulation with several kinds of additive ingredients. In particular, flexible-type shaped articles of vinyl chloride-based resins are fabricated with admixture of a relatively large amount of a plasticizer ranging usually from 15 to 50% by weight of the vinyl chloride-based resin.

One of the unavoidable problems in such a high loading of a plasticizer in shaped articles of flexible-type fabricated with a vinyl chloride-based resin is the bleeding of the plasticizer on to the surface of the shaped article in the lapse of time. The plasticizer thus exuded on the surface of a shaped article is naturally transferred to the surface of a second body which is kept in contact with the plasticizerformulated shaped article of a vinyl chloride-based resin.

For example, many electric wires are provided with an insulating layer of a plasticized vinyl chloride-based resin. The plasticizer in the insulating layer migrates toward the surface and dissipates into the atmospheric air, especially if accelerated by heat when the electric wire is used with a relatively large electric current. Such a loss of the plasticizer is of course undesirable for maintaining the good physical properties of the insulating layer. Therefore, the use of a less volatile high polymeric plasticizer is recommended particularly in the formulation for the insulating layers of electric wires.

Further, films and sheets of a plasticized vinyl chloride-based resin are sometimes subject to a serious problem of surface stain by the plasticizer exuded on the surface when, for example, the film or sheet is used as a flooring material or wall material. In addition, a phenomenon of so-calied blocking is unavoidable with films or sheets of a plasticized vinyl chloride-based resin when the films or sheets are kept stacked on each other or as a roll due to the stickiness by the plasticizer exuded on the surface.

Moreover, when a shaped article of a plasticized vinyl chloride-based resin is lastingly kept in contact with certain liquids such as oils and organic solvents, the plasticizer contained in the shaped article is extracted into the liquid in contact therewith so that the content of the plasticizer in the shaped article is decreased leading to inferior physical properties of the shaped article. Such an extraction of the plasticizer into the liquid is disadvantageous, especially, when the shaped articles of the plasticized vinyl chlorlde-based resin are containers of cosmetic materials, wrapping materials for foodstuffs, medical instruments and the like because the extracted plasticizer contaminates a solution containing oilsolubilizing ingredients such as soap solutions, foodstuffs such as milk and edible oils and physiological liquids such as blood and other body fluids.

Besides, films of plasticized vinyl chloride-based resins are widely used in the field of agriculture such as in the building of greenhouses but the bleeding of the plasticizer is also undesirable in this case because bleeding of the plasticizer causes blocking of the films or decrease in the transparency of the films to light.

The above explanation is given particularly with respect to plasticizer bleeding but the other kinds of additives used in the formulation of vinyl chloride-based resins are more or less subject to a similar problem of surface bleeding or blooming.

Various attempts have been made hitherto to solve the above described problems of surface bleeding or blooming of additive ingredients, typically a plasticizer, formulated in shaped articles of a vinyl chloride-based resin.

For example, the use of a high polymeric plasticizer such as polyester-based ones is recommended instead of conventional low molecular weight plasticizers because of their extremely low migration and extractability. Unfortunately, such a high polymeric plasticizer is inferior in its plasticizing effect in addition to the expensiveness in comparison with low molecular weight plasticizers.

Alternatively, a method has been proposed in which the surface of shaped articles of a vinyl chloride-based resin is coated with other kinds of synthetic resins such as acrylic resins, polyurethane resins, polyamide resins and the like though with the disadvantages that such an overcoating is provided only with a burdensome operation. Also the rather weak mechanical properties of the overcoating layer allow it to become peeled off during sustained use or on contact with other hard bodies.

Further alternatively, formulation in the vinyl chloride-based resin of a considerable amount of certain bleeding-preventing additives is recommended such as an aliphatic acid amide, silicone fluid, silica powder, diatomaceous earth, kaolin, talc and the like. The effectiveness of this method is not so high as desired and sufficient effects are obtained only with sacrifice of the other advantageous properties possessed inherently by vinyl chloride-based resins.

Thus, despite eager demand and extensive investigations, no satisfactory and convenient methods have been developed hitherto to effectively prevent the surface bleeding or blooming of a plasticizer and other additive ingredients formulated in shaped articles of a vinyl chloride-based resin.

The method of the present invention established as a result of the extensive investigations undertaken by the inventors comprises subjecting a shaped article of a vinyl chloride-based resin containing at least one kind of additive ingredient having a tendency to exude on the surface of the article to a treatment of irradiation with ultraviolet light having an energy distribution predominantly in the wavelength region from 105 to 200 nm in an atmosphere of oxygen or an oxygen-containing gaseous mixture of which the oxygen pressure or oxygen partial pressure is in the range from 0.05 to 50 Torr or, preferably, from 0.1 to 40 Torr.

Despite the very remarkable effectiveness of this method, the effect of the ultraviolet irradiation is limited only to a very superficial layer of the shaped article so that no adverse effects are brought about such as coloration and deterioration of the physical properties of the shaped articles.

Preferred embodiments of the invention will now be described in detail.

The shaped article of a vinyl chloride-based resin used in the method of the invention is an article shaped with a polyvinyl chloride resin or a copolymeric resin of which the major portion, say 50 % by weight or more, is composed of the monomeric units of vinyl chloride copolymerized with one or more of ethylenically unsaturated monomers copolymerizable with vinyl chloride.

The ethylenically unsaturated monomers copolymerizable with vinyl chloride are exemplified by vinyl esters such as vinyl acetate, vinyl ethers, acrylic acid and esters thereof, methacrylic acid and esters thereof, maleic orfumaric acid and esters thereof, maleic anhydride, aromatic vinyl compounds such as styrene, vinylidene halides such as vinylidene chloride, acrylonitrile, methacrylonitrile and olefins such as ethylene and propylene.

The shaped article of a vinyl chloride-based resin has at least one kind of additive ingredients which may migrate toward and bleed on the surface of the shaped article. Apart from a plasticizer which is used as a representative example, additive ingredients to be formulated are exemplified by stabilizers, lubricants, heat-stability improversfillers anti-oxidants, ultraviolet absorbers, antistatic agents, antifogging agents, pigments, dyes, crosslinking aids and modifier rubbers.

In particular, the plasticizers, bleeding of which can be substantially prevented by the method of the invention, are exemplified by esters of phthalic acid such as dioctyl phthalate, ditutyl phthalate and the like, esters of an aliphatic dibasic carboxylic acid such as dioctyl adipate, ditutyl sebacate and the like, glycol esters such as esters of pentaerithritol, diethylene-glycol dibenzoate and the like, esters of an aliphatic monobasic carboxylic acid such as acetylricinoleic acid and the like, esters of phosphoric acid such as tricesyl phosphate, triphenyl phosphate and the like, epoxidated fatty acids such as epoxidated soybean oil, epoxidated linseed oil and the like, bisphenolbased epoxy resins, esters of citric acid such as acetyltributyl citrate, acetyltrioctyl citrated and the like, trialkyl trimellitate, tetra-n-octyl pyromellitate and polypropylene adipate as well as other types of polyester plasticizers. The amount of the plasticizer in the plasticized polvinyl chloride resin composition is usually in the range from 30 to 70 parts by weight per 100 parts by weight of the resin although the amount may be reduced when the composition contains a substantial amount of rubbery elastomers.

The forms of the shaped articles include films, sheets, plates, rods, tubes, boxes and any other irregular forms in so far as the ultraviolet light can reach recessed surfaces such as the inner surface of a tubular body.

In the method of the present invention, the surface of the shaped article of the vinyl chloride-based resin is irradiated with ultraviolet light having an energy distribution predominantly in the range of wavelength from 105 to 200 nm in an atmosphere of oxygen or an oxygen-containing gaseous mixture of which the oxygen pressure or oxygen partial pressure is in the range from 0.05 to 50 Torr.

The above limitation of the range of the oxygen pressure is given since UV irradiation in an atmosphere of oxygen pressure lower than 0.05 Torr, for example, in an atmosphere of substantially pure nitrogen, argon, helium, neon and the like, cannot give a satisfactory UV irradiation effect even when the irradiation time is impractically extended. Such a prolonged UV irradiation is undesirable also because of coloration or deterioration of physical properties of the irradiated shaped article.

When the oxygen pressure exceeds 50 Torr, on the other hand, substantial extension of the irradiation time is also required in order to obtain a satisfactory UV irradiation effect. In addition, considerable amounts of ozone are produced by the UV irradiation in an atmosphere of increased oxygen pressure bringing about a serious problem of pollution of the working environment.

The wavelength limitation of the ultraviolet light is given since no desirable effect is obtained by irradiation with ultraviolet light of a wavelength longer than 200 nm while the use of ultraviolet light of a wavelength shorter than 105 nm is impractical.

It is well known in the photochemistry of polymers that irradiation of a polyvinyl chloride resin with ultraviolet light induces a dehydrochlorination reaction of the polymer chain with formation of a polyene structure which further leads to the coloration of the polymer and degradation of the polymer with scission of the molecular chains. In view of the above given common understanding in the photochemistry of polymers, it is very surprising that the ultraviolet irradiation of a shaped article of a vinyl chloride-based resin is beneficial in preventing bleeding of the plasticizer or other additive ingredients on to the surface of the article only when the ultraviolet light has an energy distribution predominantly in the wavelength range of 105 to 200 nm.

Further, it is a generally accepted practice that ultraviolet irradiation in the so-called vacuum ultraviolet region is carried out preferably in an ambient atmosphere evacuated to as high as possible vacuum to avoid absorption of the ultraviolet light by the oxygen remaining in the atmosphere or in an atmosphere replaced and filled with a gas having high transparency to ultraviolet light of the wavelength range such as nitrogen and helium. Therefore, it has been very surprising that the desired effect of ultraviolet irradiation for preventing surface bleeding of a plasticizer and other additive ingredients is best accomplished when the irradiation is carried out in an atmosphere of 0.05 to 50 Torr of oxygen in comparison with an atmosphere of high vacuum.

The type of ultraviolet lamp used as the source of the light for irradiation is not particularly important provided that the energy distribution of the ultraviolet light emitted therefrom is predominantly in the range of 105 to 200 nm. For example, rare gas-filled discharge lamps and argonmercury low pressure lamps are suitable for the purpose which are provided with a window made of a UV-transparent material such as lithium fluoride, calcium fluoride, fused quartz glass and the like. The forms of the lamps may be straight-tubular, spiral or annular. It has been noted that light components having wavelengths longer than 200 nm are not particularly detrimental in obtaining the desired irradiation effect if not excessively strong in the longer wavelength region.

The irradiation time for obtaining a sufficient effect is a function of the energy density on the irradiated surface and the type of vinyl chloride-based resin and no definite range can be given of the irradiation time because of the extreme difficulty in the dosimetry of the ultraviolet light. The energy density on the irradiated surface is in turn a function of the energy output of the lamp and the distance of the irradiated surface from the lamp. The effectiveness of the ultraviolet irradiation is also somewhat influenced by the oxygen pressure in the atmosphere. Therefore, it is a recommendable practice that the optimum irradiation time is determined by preliminary experimentation prior to production.For example, an irradiation time of 3 minutes or less is sufficient in mose cases with an argon-mercury low pressure lamp of 200 watts power placed at a distance of 1 mm to 50 cm from the irradiated surface. It should be noted that the temperature of the irradiated surface also influences the effectiveness of the ultraviolet irradiation so that the surface temperature should preferably not be excessively high.

Microscopic examination indicated that the thickness of the surface layer chemically modified by the ultraviolet irradiation according to the method of the invention is 1 m or smaller despite its remarkable effectiveness for preventing the surface bleeding of the plasticizer or other additive ingredients. Thus, the UV-treated shaped article of the vinyl chloride-based resin is substantially free from the drawbacks of surface coloration or adverse effects on the physical properties of the shaped article and the advantageous properties inherent in the vinyl chloride-based resin are retained as such.

The following Examples illustrate the method of the present invention in further detail with several comparative experiments. In the Examples, parts are all given as parts by weight.

EXAMPLE 1 (Experiments No. 1 to 7) A sheet of a plasticized polyvinyl chloride resin with a thickness of 1 mm was fabricated by compression molding at 1600C with a composition composed of 100 parts of a polyvinyl chloride resin, 50 parts of di(2-ethylhexyl) phthalate as a plasticizer, 1.5 parts of calcium stearate and 1.5 parts of zinc stearate.

The above prepared sheet was placed under an ultraviolet lamp at a distance as indicated in Table 1 and irradiated with ultraviolet light with the lamp turned on for 1 minute in an oxygen atmosphere of a pressure as indicated in Table 1. The ultraviolet lamp used here was a low pressure mercury lamp of 300 watts power with argon gas and mercury vapor sealed in a quartz glass tube emitting line spectra a wavelengths of 185 nm, 254 nm, 313 nm and 365 nm.

Each of the thus ultraviolet-treated sheets was subjected to determination of the extractable amount of the plasticizer with n-hexane by the procedure described below and visual examination of coloring induced by the ultraviolet irradiation to give the results set out in Table 1 below.

Determination of the extractable amount of the plasticizer: the sheet was placed and fixed on the bottom of a cylindrical vessel of 100 ml capacity and 50 ml of n-hexane was introduced into the vessel so as that 30 cm2 area of the irradiated surface of the sheet was contacted by the solvent. The vessel was shaken in a thermostatted water bath at 400C for 2 hours and the amount of the plasticizer extracted into the solvent was determined by gas chromatography to give a result expressed in #tg/cm2. Table 1

Experiment No. 1 2 3 4 5 6 7 Distance from 2 2 2 2 2 15 No lamp, cm irradiation Pressure of oxygen, 0.01 0.1 1 40 60 0.1 Torr Plasticizer extracted, 220 11 Less 25 540 Less 1560 Fg/cm2 than 1 than 1 Degree of Re coloration mark- Slight No No No No able On the other hand, transfer of the plasticizer from the above sheets to a polystyrene plate kept in contact with the sheet was examined with the sheet before ultraviolet irradiation and the sheet irradiated with ultraviolet light with the conditions as in Experiment No. 3 shown in Table 1. The testing procedure for the plasticizer transfer was as follows.

Determination of plasticizer transfer to polystyrene plate: The irradiated surface of a test piece of 30 cm2 area taken from the sheet sample by cutting was directly contacted with a polystyrene plate of 3 mm thickness having the same form as the test speciment and sandwiched between two glass plate and kept as such at 700C for 7 days under a load of 1.5 kg/cm2.

After the end of the above contacting period, the polystyrene plate was taken out and dissolved in toluene followed by precipitation with n-hexane. The amount of the plasticizer contained in the liquid phase was determined by gas chromatography and the result was recorded in #g/cm2. The result obtained with the above irradiated sheet was less than 1 yg/cm2 while the amount of the transferred plasticizer from the unirradiated sheet was 290 #g/cm2.

EXAMPLE 2 (Experiments No. 8 and No. 9) The same sheet of the plasticized polyvinyl chloride resin as in Example 1 was irradiated with ultraviolet light with the distance from the lamp, the gaseous atmosphere and the irradiation time as indicated in Table 2 below, the other conditions being the same as in Example 1. The thus ultravioletirradiated sheets were examined for the extractable amount of the plasticizer, amount of plasticizer transfer to the polystyrene plate and degree of coloration in the same manner as in Example 1 to give the results set out in Table 2.

Table 2

Experiment No. 8 9 Distance from lamp, cm 3 3 Gaseous Oxygen 10 Torr 160 Torr atmosphere Nitrogen 750 Torr 600 Torr Irradiation time, minutes 2 2 Plasticizer extraction, Fg/cm2 | Less than 1 990 Plasticizer transfer to polystyrene plate, ftg/cm2 Less than 1 170 Degree of coloration No No EXAMPLE 3 (Experiment No.10) The same sheet of the plasticized polyvinyl chloride resin as in Example 1 was placed 10 cm apart from a low pressure mercury lamp with mercury vapor sealed in a fused quartz glass tube having a power of 700 watts and emitting line spectra at 185 nm, 254 nm, 313 nm and 365 nm and the sheet was irradiated with ultraviolet light for 1 minute in an atmosphere of oxygen of 10 Torr. The thus irradiated sheet exhibited no coloration by visual examination and the amount of the plasticizer extraction from the sheet was less than 1 fltg/cm2 as determined in the same manner as in Example 1.

EXAMPLE 4 (Experiment No. 11) The same sheet of the plasticized polyvinyl chloride resin as in Example 1 was placed 0.5 cm apart from a 200 watts low pressure mercury lamp with argon gas and mercury vapor sealed in a fused quartz glass tube emitting line spectra at 185 nm, 254 nm, 313 nm and 365 nm and the sheet was irradiated with ultraviolet light for 1 minute in an atmosphere of oxygen of 10 Torr. The thus irradiated sheet was found to be very slightly colored and the amount of the plasticizer extraction from the sheet was less than 1 flwg/cm2 as determined in the same manner as in Example 1.

EXAMPLE 5 (Experiments No. 12 and No. 14) A sheet of 0.5 mm thickness was fabricated by compression molding at 1 600C with a composition composed of 100 parts of a polyvinyl chloride resin, 50 parts of n-octyl phthalate, 1.5 parts of barium stearate and 1.5 parts of zinc stearate.

The sheet was placed 2 cm apart from a 30p watts low pressure mercury lamp with mercury vapor sealed in a fused quartz glass tube and the sheet was irrdiated with ultraviolet light for 30 seconds in an oxygen atmosphere of 10 Torr. (Experiment No.12).

For comparison, the lamp was covered with a filter absorbing ultraviolet light in the wavelength region of 200 nm or below and the same irradiation treatment was carried out as in the above in which the ultraviolet light reaching the sheet had wavelengths longer than 200 nm (Experiment No.13).

The thus irradiated sheets and a sheet before irradiation (Experiment No. 14) were examined for the amount of plasticizer extraction, plasticizer transfer to polystyrene plate and degree of coloration in the same manner as in Example 1 to give the results set out in Table 3 below.

Table 3

Experiment No. 12 13 14 Plasticizer extraction, #g/cm2 Less 2830 2000 than 1 Plasticizer transfer to Less 430 420 polystyrene plate"lg/cm2 than 1 Coloration by irradiation No Yes

Claims

1. A method for preventing bleeding of an additive ingredient contained in a shaped article made of a vinyl chloride-based resin on to the surface of said shaped article which comprises irradiating the surface of the shaped article with ultraviolet light having an energy distribution predominantly in a wavelength region of from 105 to 200 nm in an atmosphere of oxygen or an oxygen-containing gaseous mixture of which the pressure of oxygen or the partial pressure of oxygen is in the range from 0.05 to 50 Torr.

2. A method for preventing bleeding of a plasticizer contained in a shaped article made of a plasticized vinyl choride-based resin on to the surface of said shaped article which comprises irradiating the surface of the shaped article with ultraviolet light having an energy distribution predominantly in a wavelength region of from 105 to 200 nm in an atmosphere of oxygen or an oxygen-containing gaseous mixture of which the pressure of oxygen or the partial pressure of oxygen is in the range from 0.05 to 50 Torr.

3. The method as claimed in claim 1 or claim 2 wherein the pressure of oxygen or the partial pressure of oxygen is in the range from 0.1 to 40 Torr.

4. A method for preventing bleeding of di(2-ethylhexyl) phthalate contained as a plasticizer in a shaped article made of a plasticized vinyl chloride-based resin on to the surface of said shaped article which comprises irradiating the surface of the shaped article with ultraviolet light having an energy distribution predominantly in a wavelength region of from 105 to 200 nm in an atmosphere of oxygen or an oxygen containing gaseous mixture of which the pressure of oxygen or the partial pressure of oxygen is in the range from 0.05 to 50 Torr.

5. A method for preventing bleeding of n-octyl phthalate contained as a plasticizer in a shaped article made of a plasticized vinyl chloride-based resin on to,,the surface of said shaped article which comprises irradiating the surface of the shaped article with ultraviolet light having an energy distribution predominantly in wavelength region of from 105 to 200 nm in an atmosphere of oxygen or an oxygencontaining gaseous mixture of which the pressure of oxygen or the partial pressure of oxygen is in the range from 0.05 to 50 Torr.

6. A method as claimed in claim 1 substantially as described in any of the Examples.

7. A shaped article made of a vinyl chloride based resin which has been treated by a method as claimed in any preceding claim.