CA1038247A - Foamed plastics coated with hydrophobic resins - Google Patents

Abstract

FOAMED PLASTICS COATED WITH HYDROPHOBIC RESINS

ABSTRACT OF THE DISCLOSURE
A foamed plastic prepared by coating a foamed article containing a pullulan type resin with a hydro-phobic resin.

Description

? 038247 1 This inven ion rclates to a foamed plastic prepared by coating a foamed article containing a pullulan type resin with a hydrophobic resin.
Because of their excellent properties, foamed plastics composed of thermoplastic resins such as, for example, polyolefin type, polystyrene type or polyvinyl chloride type resins have heretofore been put into various uses such as leathers, sheets, containers, furniture materials, soundproof materials, packing materials, buffer materials, matting materials, etc.
-, These foamed plastics 9 however, are so physi-cally and chemically stable that they are not decomposed ~¦ by spontaneous disruption and are quite difficultly -~1 discarded after use, and the abondonment thereof has `~ 15 become even a social problem as one of the problems concerning environmental pollution. For example, when they are buried in the ground, there occurs the depres-sion of the ground; when they are subjected to combustion treatment, there occur the secondary pollution due to 20 generation of large amounts of poisonous gases; and when they are intended to be subJected to regeneration treatment, great expenses are required for the treatment.
Further, there have heretofore been proposed such processes that the foamed plastics are incorporated 25 with photo-decomposition promotors so as to be decom-posed by irradiation with the sunlight. However, the actual sta~e is such that the said processes are being s utilized only part~y ~ccause of the facts that the foam-! ed plastics are not decomposed but ~re left as they ¦ ~0 are when shielded from the sunlight like in the case - 1 - y,~

~'', 1038Zg~7 1 where thcy are pl~ced in the shade or buried in the ground, for example, and that the decomposition promotors are costly and toxic.
The above-mentioned problems have been dis-missed by the utilization of a foamed plastic contain-ing a pullulan type resin, taking advantage of such characteristic properties of the pullulan type resin that it is non-toxic9 is edible, does not generate poisonous gases even when subjected to combustion, and - 10 can spontaneously be decomposed by microorganisms even when discarded as it is.
However, since the pullulan type resin is eg-tremely high in hydrophilic property, a foamed plastic containing the said resin is high in water and moisture - 15 absorptivity, and hence is restricted to be put into -uses where high water resistance is required.
~j ~ith an aim to overcome the above-mentioned i drawback of the foamed plastic containing a pullulan type resin~ the present inventors conducted extensive ~ 20 studies to find that when coated with a hydrophobic ¦ - resin, the said foamed plastic can be made high in water resistance while maintaining the non-pollution property thereof as it iso Based on this finding, the inventors have accomplished the present invention.
An object of the present invention is to pro-vide a foamed plastic prepared by coating with a - hydrophobic resin a foamed article composed of a resin composition containin~ a pullulan typQ resin or a l blend of a pullulan type resin with a thermoplastic ¦ 30 resin.

~038247 According to the present invention there is provided a foamed plastics material comprising a foamed article containing a pullulan type resin which is coated with at least one layer of a hydro~hobic resin.
The process for foaming the resin composition containing a pullulan type resin is not particularly limited, and may be carried out, for example, by the use of a plasticizer or foaming agent capable of yielding a vapor or gas, at a temperature above the plasticization temperature to below the decomposition temperature of said resin composition.
Examples of the plasticizer capable of yielding a vapor or gas, referred to in the above, include water; polyhydric - alcohols such as glycerin, ethylene glycol, polyethylene glycol, sorbitol, propylene glycol and polypropylene glycol; amides such as dimethylformamide and formamide; amines such as triethylenetetramine, diethylenetriamine, ethanolamine, --~ propylamine, propylenediamine, butylamine and ethylamine;
and dimethyl sulfoxide. These plasticizers may be used either singly or in the form of a mixture of two or more members. The amount of the plasticizer to be incorporated into the resin composition is not particularly limited, but is ordinarilv 1 to 70 ~leight %, preferably 3 to 50 weight %.
As the foaming agent, there may be used any of a heat-decomposable solid foaming agent, a volatile liquid - foaming agent or a gaseous foar:ling agent.
Examples of the solid ~oaming agent include organic -~ solid foaming agents such as dinitrosopentamethylenetetramine, - azodicarbonamide, '. , :.

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103E~247 1 azobisisobutyroni~ril~ p, p-hydro~yben~enesulfonyl hydrazide, and the like azo compounds which decompose at below the molding temperature. The amount of said solid foaming agent to be incorporated into the resin composition is 0.1 to 30 weight %, preferably 0.2 to 20 weight % based on t~é weight of the resin composi-- tion.
Alternatively, there may be used an organic -- acid such as citric, tartaric, diglycolic or oxalic ~ 10 acid, or an inorganic salt such as sodium carbonate, -~ potassium carbonate, sodium bicarbonate or potassium bicarbonate, which is a solid foaming agent yielding ` carbon dioxide and water. This solid foaming agent, however, is preferably used as an assistant foaming agent for making foams uniform and fine to increase the whiteness and softeness of the product. In this case, the amount of the assistant foaming agent to be incor-- porated in-to the resin composition is 0.05 to 10 weight ~, preferably in the range of 0.1 to 5 weight %.
Examples of the volatile liquid foaming agent . .. .
~ include low boiling point aliphatic ketones such as :~!
~ acetone and methyl ethyl ketone; low boiling point :, ., , :
esters such as methyl acetate, ethyl acetate, methyl ~ formate and ethyl formate; aliphatic lower alcohols such - 25 as methanol and ethanol; normally liquid low boiling point hydrocarbons such as pentane, hexane, heptane, petroleum ether, cyclopentane and cyclopentadiene; and halo~en-containin~ normally liquid ~olatile hydrocarbons such as methyl chloride, ethyl chloride, chloroform, mcthylene bromide and dichlorodifluoromethane. The -- lt --': :

103~Z47 1 amount of said volatile liquid foaming agent to be incorporated into the resin composition i9 O. 5 to 20 weight %, preferably 1 to 10 weight %.
Examples of the gaseous foaming agent include normally gaseous compounds such as nitrogenJ carbon - dioxide, helium, methane, ethane, propane, butane, ethylene, propylene and gaseous halogenated hydro- -- . carbons. The amount of said gaseous foaming agent to be incorporated into the resin composition is 0.5 to 20 ~eight %, preferably 1 to 10 weight %.
The process for coating a foamed article containing a pullulan type resin with a hydrophobic -.
. resin is not particularly limited and may be used any . known coating processes. That is, there may be adopted .s- 15 any of the process in which the foamed article contain-... ., . ~ing a pullulan type resin is previously formed, and . is then sprayed with a solution or a dispersion, such , . .; as emulsion, suspension or plastisol, of the hydrophobic ` - resin, or is immersed in a solution or dispersion of ; 20 the hydrophobic resin, thereby forming a resin coating . ,:
~: on the su~face of the said foamed article; or the pro- .
.~ cess in which a pullulan type resin-containing composition incorporated with a plasticizer for the . .
:~ pullulan type resin, and if necessary with a foaming . .,~ .
~i 25 agent, is molded at below the vapor-yielding temperature ~ of the plasticizer and below the gas-yielding tempera-f~, ture of the foaming agent to prepare an unfoamed . article, which is then sprayed with a solution or dis-:~ persion of the hydrophobic resin or i5 immersed in a solution or dispersion of the hydrophobic resin, and ,., 1 thereafter the thus treated un~oamed article i8 heated or subjected to heat generation, thereby foaming the unfoamed article and, at the same time, forming a resin coating on the said article. If necessary, the foamed article may have previously been incorporated with a - curing agent.
The pullulan type resin-containing foamed `~; article may be coated with not only one but also two or more layers of resin coatings. Further, in order to properly control the adhesion between the surface of the pullulan type resin-containing foamed article and the resin coatings and the adhesion between the - resin coatings, there may be used a suitable amount ~, of a conventional anchor coating agent, a primer or 15 an adhesive. ~ - -Examples of the hydrophobic resin referred to in the present invention include thermoplastic resins such as polyethylene, polypropylene, poly-- styrene, acrylonitrile-butadiene-styrene copolymer, 20 polymethyl methacrylate, polyvinyl acetate, polyvinyl - `
chloride, polyvinylidene chloride, vinyl acetate-vinyl chloride copolymer, olefin-vinyl acetate copolymers, polycarbonates~ polyacetals, polysulfones, polyamides, ~i and polyesters; thermosetting resins such as poly-urethanes, unsaturated polyesters and epoxy resins;
,1 and mixtu~es thereof.
The pullulan referred to in the present invention is such a high molecular weight linear polymer that units of maltotriose, which is a trimer of glucose, have been repeatedly bonded through a-linkages whlch . ~ , .. . .

1 are different rom those of said trimer, and has such molecular structure as represented by the formula, ,, .' ., - . :
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~03~Z47 1 whercin n represents the polymerization degree and i5 an integer of 20 to 10,000.
The pullulan used in the pre~ent invention is not particularly limited in process for production thereof. At present, it can be isolated and recovered as a tacky substance secreted in a culture liquor of a strain belonging to the genus Pullularia which is an incomplete microorganism. That is, a strain of the - species Pullularia pullulans is subjected to shaking culture at 24C. for 5 days in a medium containing lO~o of partially hydrolysed starch, 0.5% of K2HP04, 0.1%
1 of NaCl, 0.02~ of MgS04-7H20, O.06% of (~H4)2S04 -~ - 0.04% of yeast extract, whereby pullulan is obtained as a tacky substance secreted from the cells into the culture liquor. If necessary, the cells are removed by centrifugation from the culture liquor, and the supernatant is subjected to methanol precipitation and separation, whereby purified pullulan can be obtained. Pullulan somewhat differs in physical pro-perties depending on the kind of strain used. In thepresent invention, however, the said difference is not greatly concerned with the properties of the resulting foamed article.
The molecular weight of the pullulan used in the present invention is not particularly limited, but ~i is ordinarily 10,000 to 5,000,000, preferably 30,000 to l,OOO,OOG.
While thc pullulan is easily soluble in cold water, it is well known that lt can be varied in water solubility when modified by etherification, esterification ~1 I _ 9 _ ,~

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10382~7 1 or graft-copolymerization with a vinyl compound. ~ihen coated with a hydrophobic resin, a foamed article obtain-ed from a resin composition containing the thus modified pullulan can also give an excellent foamed plastic, like in the case where pullulan is used. Accordingly, the pullulan type resin referred to in the present invention includes not only pullulan but also a partial-ly modified pullulan prepared by subjecting pullulan to - etherification~ esterification, phosphatization, oxida-tion, or graft-copolymerization with styrene or vinyl chloride O , ,~
The foamed plastic of the present invention, which is obtained by coating a pullulan type resin-containing foamed article with a hydrophobic thermo-plastic or thermosetting resin, lS hieh in water -resistance by virtue of the hydrophobic property of ~ : said resin. On the other hand, the foamed plastic of -~ the present invention can be easily abandoned. That - is, when the foamed plastic is subjected to combustion, it generates less amount of heat, due to the character-istic properties of the pullulan type resin, to make it possible to prevent the incinerator from damage, while when the foamed plastic is abandoned by allowing it to stand in the natural world, the resin coating of the foamed plastic is marred or peeled off to expose the pullulan type resin-containing foamed article, where-by the foamed article becomes easily decomposable both in water and in ground by dissolution in water or by ~ decomposition with microorganisms. Thus, the foamed~
! 30 plastic of the present invention can be said to be a ;

:` ~038247 1 pollution-free foamed plastic.
For further clarification, the present invention is illustrated in more detail below with reference to examples, but the invention i9 not limited 5 to the examples.

Example 1 100 Parts by weight of a dry pullulan powder e (molecular weight 50,000) was homogeneously mixed with ~; 30 parts by weight of water, and the resulting mixture 10 was melted for 10 minutes by use of a hot press (90C., `100 kg/cm2)9 and then cooled by means of a cold press to prepare a sheet of 3 mm. in thicknessO This sheet ~1 :~ was heated-for 10 minutes in a hot air recycle type -~ dryer at 180C. to obtain a foamed article having a - 15 foamed ratio of 3 times the original volume. The foamed - article thus obtained was ;mmersed in a plastisol of ` vinyl chloride resin, and then again heated for 10 minutes in a hot air recycle type dryer at 180C.
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~ After cooling to room temperature, the resulting foamed -~ 20 plastic was dipped in water for 3 hours, dried and then measured in weight loss to obtain a value of 0.05~.
The composition of the plastisol of vinyl ~i chloride resin used was as follows:
~ Vinyl chloride resin (Sumilit t~. 25 P x N, produced by Sumitomo ; Chemical Co., ~td.; polymeriza- 100 parts by welght ~- tion degree; 1300) Plasticizer (dioctylphthalate) 60 ~,' .2 , ..

1~38Z47 1 Sta~ilizer (tradename: KP-150 pro~uced by Kyodo Phcrmaceutical 2 parts by weight Co., complete stabilizer containing Cd Ba and Zn) Comparative Example 1 ~ he same foamed article as in Example 1, which had not been coated with the vinyl chloride resin, - was dipped in water for ~ hours 9 whereby the foamed article was dissolved completely.
.

E~ample 2 An acetylated pullulan powder (molecular weight ~ 35,000) containing 15 weight % of water and 5 weight ~0 `~ of ethylene glycol and having a substitution degree of 0.5 (complete substitution degree 3.0) was mi~ed with 20 weight %, based on the weight of the total resin, of a polyethylene (Sumikathene ~ L 705~ produced by - Sumitomo Chemical Co , ~td.; density 0.92 g/cm3, melt ~ inde~ 7). The resulting mixture was sufficiently -~l admixed by means of a mixer and then subjected to .1 ~; 20 compression molding at 140C. to prepare a sheet of t~
160 mm x 160 mm x 3 mm in size. This sheet was subject-ed to a high frequency voltage of 2,450 MHz for 3 minutes in a microwave oven to obtain a sheet composed of uniform cells and having a foamed ratio of 2.5 times , ~j 25 the original volume. The sheet thus obtained was dipped . in a 10 weight % benzene solution of polystyrene, and then all~wed to st~nd ~or 1 hour in a hot air furnace -~ at 100C. to remove the solvent, thereby formin~ a polystyrene coating on the said foamed sheet. After . i~ ~
' ~ ' 1 cooling to room temperature, the resulting sheet was dipped in water for ~ hours, dried and then measured ; in weight loss to obtain a value cf 0.08%.

Comparative Example 2 The same foamed sheet as in Example 2, which was composed of acetylated pullulan and polyethylene . and which had not been coated with polystyrene, was dipped in water for 3 hours, whereby the sheet was ' dissolved so completely as not to retain its original :~' 14- shape 9 and only the polyethylene was leftO

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Claims (7)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A foamed plastics material comprising a foamed article containing a pullulan type resin which is coated with at least one layer of a hydrophobic resin.

2. A foamed plastic according to Claim 1, wherein the hydrophobic resin is at least one member selected from the group consisting of thermoplastic resins and thermosetting resins.

3. A foamed plastic according to Claim 2, wherein the thermoplastic resins are polyethylene, polypropylene, polystyrene, acrylonitrile-butadiene-styrene copolymer, polymethyl methacrylate, polyvinyl acetate, polyvinyl chloride, polyvinyl-idene chloride, vinyl acetate-vinyl chloride copolymer, olefin-vinyl acetate copolymers, polycarbonates, polyacetals, poly-sulfones or polyesters.

4. A foamed plastic according to Claim 2, wherein the thermosetting resins are polyurethanes, unsaturated polyesters or epoxy resins.

5. A foamed plastic according to Claim 1, wherein the pullulan type resin is pullulan or a partially modified pullulan.

6. A foamed plastic according to Claim 5, wherein the partially modified pullulan is selected from the group consisting of an etherified pullulan, an esterified pullulan, a phosphatized pullulan, an oxidized pullulan and a graft copolymer of pullulan with styrene or vinyl chloride.

7. A foamed plastic according to Claim 1, wherein the molecular weight of the pullulan type resin is 10,000 to 5,000,000.