CA1301990C - Polyvinyl chloride resin composition for molding - Google Patents

Abstract

A B S T R A C T

POLYVINYL CHLORIDE MOLDING POWDER

The use of C5-C8 alkyl group fatty acid metal soap, particularly a mixture of barium and zinc such metal soaps, to stabilize polyvinyl chloride powder molding compositions against mold staining. The compositions preferably also include magnesium compound stabilizer to improve amine resistance when the molded product is to have polyurethane foam formed in situ thereon.

Description

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POLYVINYL CHLORIDE MOLDING
POWDER

The present invention relates to a polyvinyl chloride powder molding composition, e.g. for making covering material for automobile inner parts such as crash pads, armlrests, head xests, console boxes, metex covers and door trims. In recent years there has been increasing demand for latter such items of complicated shape which are ligh-~ in weight, have embossed or stitched patterns, and are soft and high-quality to the touch.
Hitherto, there have been two kinds of covering material, one being vacuum-ormed from plasticized sheet composed mainly of polyvinyl chloride resin and ABS resin, and the othe being rotationally molded- or slush-molded from paste sols composed mainly of polyvinyl chloride paste resin and plasticizer.
l`he vacuum-o~ned product meets the requirement for light weLght, but is hard to the touch. Besides, it is extremely diffioult to obtain vacuum-formed products of complicated shape havirlg embossed or stitched patterns of high-guality feel. ~1e vacuum-formed product also has the defect that, because of its large residual strain, cracks are easily formed during long-term use.
On the other hand, the sol molded product has a soft feel, but the sol, because of its low gelation temperature, rapidly melts in the mold so that phenomena such as flow mark, lip, stringiness of the sol, etc. appear. The sol molded product, therefore, has the defects that its inside surface lacks smooth-~ '~

~0~9~:3 ness, that it may be too thick, and sol removal from the mold takes too long~
The 501 also has the problems that a great deal of labor is required in cleaning tanks, pipes, etc. for color change, and that its viscosity changes with lapse of time so that it can not stand long-term storage. I
In recent years, powder molding methods have a~tracted public attention as a means to solve these defects and problems.
The powder molding methods include fluidized bed coating, electrostatic coating, powder flame spray coating, powder ro~atlonal molding, powder slush molding and the like.
A powder composition used in these techniques should he free-flowlng and of good moldabllity.
It is well known to produce powder compositions by dry-blending polyvinyl chloride resinsl plasticizers, ~tabillzers, pigments, fillers and auxilliaries etc. on blenders or high speed rotating mixers equi.pped with a heating jacket.
It is al50 well known ~o add smal1 amounts of polyvinyl chloride resin fine powders or inorganic fillers such as calcium carbonate fine powders, etc. in order to improve the flowabili~y ~Rubber Digest, Vo1~14, No.8, 32 - 40; Polyvinyl Chloride ~ Its Chemist~y and Industry - II, pp.367 - 370, 1968; and Japanese Patent Publication No.157511962).
In powder molding, a polyvinyl chlorlde powder composi-tion is molded in a mold kept at high temperatuxes, so that the surface of the mold i5 gradually stained as the number of molding shots increases. Conse~uently, molding works must stop operation .

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temporarily fox mold cleanins, as a result of which productivity is markedly reduced and extra labor is required for cleaning.
When the mold is heaviIy stained, the molded covering material becomes difficult to detach from the mold, stains on the mold S are transferred to the sur~ace of the coverin~ material, and in some cases, the thickness of the molded material becomes too great.
It is therefore very important industrially and econom-ically to develop polyvinyl chloride powder compositions which produce less stain on molds, in other words, are superior in resistance to mold staining.
To this end, after extensive study, we found it desirab1e to use in such powder compositions a stabilizer comprising the metal soap of a fatty acid having a C5-C8 alkyl group.
In its most preerred aspect, the invention pxovides a polyv.tnyl chloride powder molding compdsition ~usually a dry blend with one or more of plastiaizers, stabil.izers, pigments and others such as fil.lers and au~iliaries added as need arises], contai.ning barium and æinc fatty acid soap stabilizers selected from -~ose of the formula:

( RC00)2Me wherein R represents a C5-C8 alkyl group and Me represents barium and zinc. This stabilizer is preferably present in an amount of 0.1 to 10 w/w ~. based:on the polyvinyl chloride resin. It preferably contains the barium and zinc fa-tty acid soaps in bariunl:
25 zinc meta]. wei.ght ratios of 1:2 to 5:1.
In po~der molding, since polyvinyl chloride powder comp~sitions are molded in a mold kept at high temperatures, too ''"' ~3~99C~
,, great an importance has been put on the thermal resistance of the composition. ~s a result, it has been normal to use the same metal soap stabilizers as for common extrusion and calendering, i.e. the metal soaps of fatty acids having alkyl groups of not less than 9 carbon atoms, for example stearates ~C17H35COO-~, pa1mitates (C15H31Coo-~, laurates ~CllH23COO-~, caprates ~Cg~1gCOO~), etc. We have appreciated, however, that powder molding is different from common extrusion and calendering in that the powder is brought in~o contact with the mold at high temperatures for only a short time, and that little shear is applied to the powder. The popularly used stabilizers, comprising the metal soaps of fatty acids having alkyl groups of not less than 9 carbon atoms, are of a powdery form in many cases.
In powder molding, however, we have found that such stabilizers are poor in dispersibility and, because of their high melting points,: do not melt sufficiently but remain in part as powder.
We also found that, even when the above known stabilizers are well kneaded with liquids such as solvents, plasticizers, etc., compatibility with the PVC is poor and also the plate-out phenomenon occurs; when the mold has fine embossed or stitched surface patterns, occurrence of this plate-out phenomenon makes it very troublesome to remove stains from the mold.
On the other hand, the metal soaps df fatty acids having alkyl groups of not more than 8 carbon atoms, for example nonanoates [C8H17COO-~, octanoates ~C7~15COO ~, heptanoates ~C6H13COO-~, bexanvate5 [C5HllCOO-~, etc., ~3~
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have less thermal resista1lce and ll~ricating action and are difficu1t to produce, and so are not generally used in common extrusion and calendering - at 1east, no-t in the substantial absence of metal soap of fatty acid having an alky]. group of not less than 9 carbon atoms.
The present invention thus provides a polyvinyl chloride powder molding composition resistant to mold staining, including metal soap of a fatty acid having a C5-C~ al]yl group; the metal moiety of such soap is preferably barium and zinc. Suitable `) 10 barium-containing soaps include barium nonanoate, barium octaboate, barium heptanoate and barium hexanoate. Suitable zinc-containing soaps include zinc nonanoate, zinc octanoate, zinc heptanoate and æinc hexanoate.
In the present invention, the barium-cont~ining and zinc-containing stabilizers are best used in combination, preferably at a metal wei~ht ratio of barium to zinc of 1:2 to 5:1.
When æinc is in excess relative to barium, e.g. thLs barium:~inc weight ratio is smaller than 1:2, there is danger ;.~ of inadequate thermal resistance, formation of black specks and focuning of the molded covering material. Such weight ratio is not therefore preferred.
Contrary to this, when barium is in excess relative to zinc, e.g.this barium:zinc weight ratio is larger than 5:1, initial coloration on moulding tends to ~ecome strong, particularly a tendency to be colored red. As a result, since the color of the molded covering material deviates from that desired, color matching becomes difficult.

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The amount of the barium/zinc-containing stabilizer used is preferably ~rom 0.1 to 10 parts by weight based on 100 parts by weight of polyvinyl chloride resin; when it is less than 0.1 part by weight, the thermal resistance may be inadequate;
when it is more than 10 parts by weight, there is a danger of the stabilizer bleeding to the surface of the moldad covering material, and the cost may increase to become uneconomic.
In order to provide as a final product a covering material for automobile im1er parts, polyurethane can be formed in place on the inside surface of the molded covering material.
In thls in situ polyurethane foaming, it is well known to use a first component composed mainly of polyol, water, foaming agent, catalyst and other auxiliaries, and a second component composed mainly of polyisocyanate.
In this polyurethane foaming, amine compounds are used as cat.alyst, e.g. ethylenediamine, triethylenediamine, triethylenetetramine, triethanolamine, etc~
these may he used alone or in combination, and as addition products with alkylene oxides such as ethylene oxide, propylene oxide, butylene oxide, epichlorhydrin~ styrene oxide.
These amine compounds, on contact with the polyvinyl chlorida covering material, markedly promote discoloration and deterior-ation o~ the material.
Consequently, there has been a need for polyvinyl chloride powder molding compositions resistant to discoloration and deterioration by amine compounds ~hereinafter referred to as amine resistance). We have found that our PVC powder molding composition is improvad in amine resistance by inclusion of magnes~um compound, preferably in an amount of from 0.1 to 5 parts by weight per 100 parts by weight of polyvinyl chloride resin.
In the development of our polyvinyl chloride powder compositlon superior in amine resistance, we examined the thermal resistance ~gear oven 110C) and light fastness (sun-shine weather-0-meter or fade-0-meter; black panel temperature, 83C) of a two-layer sheet comprising the polyvinyl chloride covering material and polyu~ethane foamed in situ, and found that the zinc compound has an ability to prevent discoloration by amine compounds. We believe the reason for this to be as follows : in systems whereln a polyvinyl chloride resin and an amine compound coexist, dehydrochlorination is promoted or a complex co~npound is formed by reaction between the resin and the amine compound to develop a characteristic color; but when a zinc stabilizer i9 present in the system, another complex compound is formed from the stabilizer and the amine compound, and in this case, a complementary relationship applies between the colors of the complex compounds to produce a harmless color. The invention, however, is not bound by theory.
In the foregoing thermal resistance and light fastness tests on the polyvinyl chloride/polyurethane two-layer sheet described above, we sought 3 method to maintain the discoloration resistance for longer, and after extensive study found that amine resistance can be improved by including a magnasium compound. We also found that the use of magnesium compound is ~ ~`r ~cJe ~ ~nC~ S

~3~)~99~3 accompanied by improved maintenance of adhesion strength between the polyvinyl chloride covering materlal and polyurethane layer even after prolonged thermal resistance and light fastness tests.
Suitable magnesium compounds for use in the present invention include for example magnesium oxide, magnesium hydroxide, magnesium phosphate, magnesium perchlorate, basic magnesium carbonate, magnesium/aluminum compounds ~e.g. hydro-talcite) and the like. These compounds may be used alone or in combination.
The amount of the magnes1um compound used is preferably in the range of O.l to 5 parts by weight based on 100 parts by weight .. . . .
of polyvinyl chloride resin. -When said amount is less than 0.1 part by weiyht, the improvement in amine resistance and the adheslon strength of the polyvinyl chloride/polyurethane two-layer sheet after the aging tests may be insu~ficient.
When said amount is more than 5 parts by weight, the ilm strength o~ the polyvinyl chloride covering material may be insufficient, and the initial coloratlon of the material on molding tends to be strongly reddish, so that such amount is not preferred.
The stabilizers used in the present invention may be added when dry-blending the composition. In this case, they may be added alone, or with one or more components selected from solvents, plasticiæers, epoxy compounds, antioxidants, photo-stabilizers, ultraviolet absorbers, phosphorus chelaters, 9g~

alcohols and pigments.
The stabilizers used in the present invention may be used with small amounts of other stabilizer or inorganic compound described below. Such other stabilizers are metal soaps other than those of Eatty acids having an alkyl group of not less than 9 carbon atoms, and include for example calcium, magnesium, barium, zinc and aluminum metal soaps of monohydric carboxylic acids (e.g. benzoic acid, toluic acid, acetyoxy-benzoic acid)and dihydric carboxylic acids te.g. oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, sebacic acid, phthalic acid). The inorganic compounds include for example caxbonates, phosphates, phosphites, silicates, calcium carbonate fine powder, aluminum hydroxide, alumina~silica sol, perchlorates and the like.
The polyvinyl chloride resins usable in ~ e present invention include vinyl chloride homopolymers, copolymers of vinyl chloride wlth ethylene, propylene or vinyl acetate and graft copolymers of vinyl chloride with ethylene/vinyl acetate aopolymer ~EVA). These polymers and copolymers can be produced by suspension polymerization, bulk polymerization or e~ulsion polymerization, and they may be used alone or in combina~ion.
The polyvinyl chloride resins for the present invention are not limited to these polymers and copolymers.
As plasticizers for use in the pxesent invention, there are given for example phthalic acid esters such as dibutyl phthalate, dioctyl phthalate, diisodecyl phthalate, diisoundecyl phthalate, etc.; trimeLlitic acid esters such as trioctyl tri-, .

o mellitate, tri-2-ethylhexyl trimellitate, tridecyl trimellitate, etc.; adipic acid esters such as dioctyl adipate, diisodecyl adipate, etcO; phosphoric acid esters such as tricresyl phosphate, trioctyl phosphate, etc., epoxy plasticizers and liquid polyesters. The plasticizers suitable are not limited to these compounds. I
As the polyol, catalyst, foaming agent, polyisocyanate, etc. for the in situ polyurethane foaming, the well known ones commonly used in the production of polyurethane foams are adequate, there being no special limitation.
The present invention is illustrated specifically by the following Examples, which are not however to be interpret2d as limitlng the invention.

To a 20-lliter super-mixer WAS added 2 kg of a straight polyvinyl chloride resin having an average polymerization degree of 700 produced by conventional suspension polymerization ~Sumilit ~ SX-7GL; produced by Sumitomo Chemical Co.). Separately from this, 25 g of barium octanoate and 25 g of zinc octanoate, 70 g of epoxidized soybean oil and llO g of a g~ay pigment contalning 3 g of a thioether antioxidant ~Antigen ~ OS; produced by Sumitomo Chemical Co.) and 2 g of a ul~raviolet absorber (Viosorb ~
580; produced by Kyodo Yakuhin Co.) were thoraughly dispersed in 400 g of trioctyl trimellitate. This dispersian liquid and then l kg of trioctyl trimellitate were added to the super-mixer while stirring at a controlled revolution speed, and the mixture was dried by heating.

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After cooling, the dried product was uniformly mixed with 200 g of a polyv1nyl chloride pas~e resin fine powder produced by the micro-suspension method ~Sumillt ~ PXQL; produced by 5umitomo Chemical Co~) to produce a powder-composition ofgood flowability.
lU0 Grams of this powder composition was sprinkled for 10 seconds on a nickel mirror plate ~100 mm X100 mm X3 mm thick ~ kept at 220 C on an electric hot plate. The mirror plate was then taken off the hot plate, and after removing the unmolten powder, th~ mirror plate havinq the molten resin' attached thereto was again placed ~n the hot plate and heated for 30 seconds to complete fusion.
After cooling and removing the formed sheet, the mirror plate was again placed on the hot plate and the above procedure was'repeated five times. After the test,'the degree o~ aloudiness of the mirror platc was examined ko find that the plate had little cloudiness, snowing a"good appearance.
xample 2 A powder composition was prepared in the same manner-~s in ~xample 1 but using 120 g of a liquid comprising 60~ of dodecylbenzene and as a stabilizer, 40% of barium/zinc octanoate previously adjusted to a barium:zinc metal we,ight ratio of 2:1. The Example 1 test was repeated five times on the same hot plate, and the degree of cloudiness of ~he nickel mirror plate examined; it was found that the plate had little cloudiness, precisely as in Example 1, showing a good appearance.
Example 3 A powder composition was prepared in ~he same manner as in Example 1 but using as a stabilizer 120 g of the barium/zinc octanoate used 1n Example 2 and 4 g of magnesi~m.oxide. The Exam~le 1 test was repeated five times.on the same hot plate, and the degree of cloudiness of the nickel mirror plate examined;
it was found that the plate had little cloudlness, precisely as in Example 1.
Ex~ le 4 A powder composition was prepared in the same manner as in Example 1 but using as a s~abilizer 120'g of the barium/zinc octanoate used in Example 2.znd 4 g of magnesium hydroxide.
The Ex.1 test.was re~eated ~.ive times on the-same hot plate, and the degree of ~loudiness of the nickel mirror plate e~camined;
it was found that the plate had little cloudiness, precisely as in Example l.
' _xam~ Q S
A powder composition'was prepared in the same manner'as in Example 1 but using as a stabilizer 120 y of the barium/zinc octanoate used in Example 2',`4'g of magnesium hydroxide and'4'g of' hydrotalcite IDHT-4, produced by Xyowa Kagaku Co.). The Ex.1 test ':~' 20 was.repeated f1ve times on the same hot plate, ~nd the.degree of cloudiness oF the nickel mirror plate examined; it was ~~ou'n'd~that the 'plate' had'littlë cloudiness , precisely as in Example 1. '' .Comparative example 1 ~he procedure was carried out in precisely the_same manner as'in Example i but using 40 g of barium stearate and 40 g.of...zinc e-~Q~k 99~1 stearate as a stabilizer. The result of the test was unsatis-factory, and white thin film-like stalns were obser~ed 'on the surface of the mirror plate.
Comparative example 2 .
The procedure was carried out in precisely the same manner as in Example l but using 40 g of barium stearateland 35 g of zinc laurate as a stabilizer. The result of the ~est was unsatis-~actory, and white thin film-like stains were observed on the surface of the-mirror plate as in Comparative example 1.
'~ Com~arative~example'3-The procedure was carried out in precisely the same manneras in Example l but using 35 g of barium laurate and lO g of zinc octanoate as a stabilizer. The result of the test ~as less sati'sfactory than 'the results'of Examples~l' to--~4-,'--and slightly white thin film-like' stains were observed on the surface of 'the mirror plate.
Comparative example 4 The procedure was carried out in precisely the same manner --as in Example 1 but using 24 g o barium stearate, 12 g of bar'ium palmitate, 4 g of barium laurate and 40 g of zinc stearate as a stabiiizer and 4 g of magnesium hydroxide. - The result of-ehe test was unsatisfactory, ~a in Comparative example 1.
~omparative example 5 , . .. __ The procedure was carried out in precisely the same manner as in Example -l but using ~4-g-of ba~ium s~earate,-12 g of barium palmitate, 4 g of ~arium laurate and 40 g of zinc stearate as a L9~

stabilizer, 4 g of magnesium hydroxide and 16 g of hydrotalcitç
DHT-4 (produced by.Kyowa Kagaku Co.). The result of the test was also unsatisfactory, as in Comparati~e example 1.
The po~der compositions obtained in Examples l to 5 and Comparative examples l to 5 were formed into shee~ as described below, and the amine resistance was tested. I
500 Grams of. powder composition was sprinkled on -an electroformed nickel plate with embo6sed patter~ ~300 mm X 300 mm) ' kept at 220C~in a furnace wherein the atmospheric temperature lo was 300C; and after 10 seconds the plate was taken from the furnace and the un~olten powder was..removed. ~he plate having the m'olten'po~der attached thereto was' agaih~placed'in the furnace and heated for-one-minute--at--an atmospheric tempera`ture of 300C td complete fusion.
After cooling, the formqd sheet was removed.. . . ~he thickness of~the sheet was 1 mm on average.
__ __. Ther~a~ter,.the formed.sheet.was placed, with its embossed --surface downwards, on an aluminum support ~rame ~300 mm X300 mm X
lO mm th'ick ~ plac~d on an aluminum foaming plate. Separately from this, water, triethanolamine and triethylenediamine were added to polyol composed mainly of glycerin/propylene oxide and glycerin/
ethylene oxide adducts to prepare a mixture. I'nto the~above sUpport frame were..injected this mixtu~e and polymeric MDI-having an NCO content of 30.5% so that the total amount was 153 g and the ' weight ratio of former to latter was 100 par~s to 50 parts by weight, whereby a polyurethane foam firmly adhered to 9o the back surface of the sheet was obtained. This polyurethane foam had a thickness of 10 mm and a foam density of 0.16 gtcm3.
This polyvinyl chloride/polyurethane two-layer sheet was cut into a desired si~e of 70 mm X150 mm to prepare a test sheet.
~our pieces of the test sheet were placed in a gear oven wherein the atmosphere was kept at 110C; one test piece was taken out every 100 hours, and a 400-hour thermal discoloration test was carried out. Similarly, four pieces of the test piece were placed in a Sunshine weather-O-metèr, wherein the temeerature of the black panel was adjusted to 83C ; one test piece was taken out every lOO hours, and a 400-hour photo-discoloration test.was carried.out. ~he resistance to thermal discoloratIon and photo~discoloration was expressed by grade using the gray scale.
; l'able 1 ~esistance to mold staining and amine resistance . . __ __ Resistance to ~mine resistance ' mold staining ~esistance to Resistance to . thermal dis- photo-discolor-. colorationation ~grade) ~grade~
_ . _ ~_ Exampl~ 1 . O . 3 4 -3 a - 2 3 4--3 ~- 3 . O ~ . ~ 5~4 . Q 41 5~4 ~ 5 C~ . 4 5~4 Comparative . .
example~l ~ 3 4 - 3 3 ~ 3 ~ -3 . _ _ _ _ 4 5 -4 ~L3~1~9~

Note 1 Assessment of reslstance to mold staining : according to the degree of cloudiness of nickel mirror plate.
0 Little cloudiness is observed.
~ Cloudiness is observed to some degree.
X Marked cloudiness is observed.
Note 2 Assessment of amine resistance :
~hermal resistance : Gear oven, 110C x 400 hours.
Li~ht fastness : Sunshine weather-0-meter, 83C x 400 hours.
Assessment of discoloratio~ : according to the grades on the gray scale.

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Claims (5)

1. A PVC powder molding composition containing 0.1-10 parts by weight (based on 100 parts by weight of PVC) of a stabilizer comprising a mixture of barium and zinc fatty acid soaps represented by the formula:
(RCOO)2Me wherein R is a C5-C8 alkyl group and Me is barium and zinc, the weight ratio of barium to zinc (calculated as metal) being 1:2 to 5:1.

2. A composition according to claim 1 including at least one magnesium compound stabilizer selected from the group consisting of magnesium oxide, magnesium hydroxide, magnesium phosphate, magnesium perchlorate, basic magnesium carbonate and magnesium/aluminum compounds.

3. A composition according to claim 2 containing from 0.1 to 5 w/w % of said magnesium compound stabilizer based on the weiyht of polyvinyl chloride.

4. A molded product of a composition according to claim 1, 2 or 3.

5. A molded product according to claim 4 with polyurethane foam formed in situ on one face thereof.