CA2087661A1 - Low temperature moldable powder for powder molding, power molding method using the same and molded article thereof - Google Patents

Abstract

LOW TEMPERATURE MOLDABLE POWDER FOR POWDER
MOLDING. POWDER MOLDING METHOD USING THE
SAME AND MOLDED ARTICLE THEREOF
ABSTRACT OF THE DISCLOSURE

A low temperature moldable powder for powder molding comprising a thermoplastic resin or thermoplastic elastomer composition, said resin or composition having a complex dynamic viscosity ?* (170°C) of 1.5 x 105 poise or less, as measured at an atmospheric temperature of 170°C and a complex dynamic viscosity ?* (250°C) of 5.0 x 104 poise or less, as measured at an atmospheric temperature of 250°C, in dynamic viscoelasticity measurements at a frequency of 1 radian/sec and a temperature average viscosity index k, calculated from the following formula, of 10 or less:
k = ?* (170°C)/?* (250°C)

Description

LOW TEMPER~TURE MOI~DABI~E POWD~R FOR POWDER
MOLDING, POWDER MOL~ING METHOD USING THE
SA~IE AND MOl:~)~ ARTICLE 'l'~l~;REOF

sAcKGRouND OF THE INVENTION
1. Field of the Invention The present invention relates to a powder for powder molding which is moldable at a lower temperature than that for conventional powders, a powder molding method using the same and a molded article thereof.
More specifically, it relates to a powder for powder molding, preferably powder molding such as powder slush molding, which is suitable for use, mainly, as IS covering materials and housings for molded articles in various fields, irrespective of backing materials, a powder molding method using the same and a molded article thereof.
2. Description of the Related Art With regard to covering materials used as interior decorative materials for automobiles, there is an increasing demand for those which have a light weight and a good and soft feeling, and which can b~ glven an embo~sed pattern or stitch pattern to increase the value 2S of molded articles. Also, during the scrapping of cars, acidic substances are generated by a combustion of such interior decorative materials to cause a contamination of the air, and thus create serious social problems such as acid rain, etc., and therefore, there i5 a strong demand for non-polluting materials.
Known covering materials of the prior art are vacuum molded olefin type thermoplastic elastomer (hereinafter called TPO) sheets and vacuum formed sheets composed mainly of vinyl chloride resins and ABS resins, or rotational molded or slush molded sols composed mainl~
of vinyl chloride resins for paste and plasticizers (hereinafter called sol moldings).

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vacuum formed TPO sheets attain the objects to provide a light weight and non-polluting material, but it is difficult to impart complicated shapes thereto.
Also, vacuum formed sheets contain a high residual molding stress caused during the forming process, and thus have a drawback in that cracks will appear after long texm usage.
vacuum formed sheets composed mainly of vinyl chloride resins and ABS resins have drawbacks similar to those of vacuum formed TPO sheets in that it is difficult to impart complicated shapes thereto, and further that, compared with TPO, they have the drawback of heavier weight and cause pollution.
Sol moldings composed mainly of vinyl chloride resins for paste and plasticizers give a soft feeling, and complicated shapes can be imparted thereto. However, since the gellation temperature is low, they melt rapidly while being molded, and thus many drawbacks arise, for example, problems in the processing such as flow marks, lip or a sol fiber-forming phenomenon, the inherent ~roblems of vinyl chloride such as a heavier weight and pollution, and further problems in that the inner window glass surface of automobiles proauced from said sol - moldlng suffer~ from hazy appearance due to the use of a large amount of plasticizers.
Due to these drawbacks and problems of the molding method, the powder slush molding method has recently attracted attention.
Powder molding methods include, in general, a flow dipping method, an electrostatic coating method, a flame s~ray coating method, a powder rotational molding method, and a powder slush molding method, and particularly for an interior decorative materlals for automobiles, the powder rotary molding method or the powder slush molding method is most sui~able.
f A partially crosslinked TPO composition is 7 known fror ~apanese Unexamined Patent Publications ~,' i .
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(Kokai) Nos. 48-26~38, 53 149240, but the known molding methods currently used for the partially crosslinked TP0 are:
a. injection molding (shear rate during processing: y 2 103 sec~l);
b. extrusion molding (lol < y < lo2 sec~l);
c. calendering (102 < y < 103 sec~l);
d. compression molding of the primarily processed product in b. or c.; and e. vacuum forming of the primarily processed product in b. or c., but all of these methods require the molding temperatures are higher or equal to the softening point, and the molding pressures must be varied depending on the viscosities and the shear rates corresponding to the respective processing conditions.
Nevertheless, in the molding method such as a powder rotary molding or a powder slush molding at a shear rate of 10 sec~l or less or under an approximately stationary state of the polymer, at a vibration frequency of 1 radian/sec., and with no application of a pressure or under a very low pressure (~ 1 kg/cm2~, the flowabllity becomes extremely poor, and accordingly, the molding becomes very difficult. Further, even if molding is possible, the poor flowability in the low shear rate region cause an incomplete thermal fusion between powder particles, and only molded articles with a low mechanical strength can be obtained.
To solve these problem~ mentioned above, Japanese UnexamiDed Patent Publication (Kokai) No. 2-57309, for example, discloses the following inventions. An embossed thermoplastic elastomer molding and a method of preparing the same, having an emboss pattern formed on the surface by melting a thermoplastic elastomer powder comprising a , 35 polyolefin resin and an ethylene-a-olefin copolymer rubber into a flowing plasticized state in a roating and heated mold with an emboss pattern.

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According to this method, however, the flowability of TPO powder in the low shear rate region is still poor, and therefore, the thermal fusion strength between powder particles is too low, causing a problem that pinholes, etc. may be formed. Moreover, molding at low temperature is impossible and a molding having a fully satisfactory appearance and physical properties, etc., has not been obtained.
Furthermore, for example, ~apanese Unexamined Patent Publication (Kokai) No. 4-lO911 discloses a thermoplastic elastomer molded article having an emboss pattern, prepared by allowing a thermoplastic elastomer powder obtained by dynamically heat treating a mixture containing a crosslinking agent and polymer particles which comprise a crystalline olefin polymer portion and an amorphous olefin polymer portion and which have an average particle size of at least lO ~m and an apparent bulk density of at least 0.2 g/ml to closely adhere to and melt the powder on the internal surface af a mold for transferring an emboss pattern in a fluidized plastic state, of which mold is in a rotating and heated state, to form an emboss patterrl thereon, and a method for ~roducing the same.
However, also in this case, the flowability of TP0 powder in the low shear rate region is insufficient, and the same problems as described above arise. A~ a result, a sufficiently satisfactory molded article has not been obtained.
Furthermore, for example, Japanese Unexamined Patent Publication (Kokai) No. 2-57310 discloseg an emhossed thermoplastic elastomer molding and a method of preparing the same, having an emboss pattern formed on the surface produced by spraying of a thermoplastic elastomer powder comprising a polyolefin resin and an ethylene-a-olefin copolymer rubber onto the inner surface of a heated mold with an emboss pattern, thereby meltiny and a~hering said powder to the inner surface of said mold.

5, :.' According to this method, however, because the powder is fed by a spray gun and adhered to the inner portion of the mold, problems arise in that the sheet thickness of the molding becomes nonuniform, and that pinholes may be for~ed.
Also, because the powder is sprayed onto a previously heated mold in the open state without being close contact with the powder feeding box and adhered to the inner surface of the mold, the problems arise of a scattering of the powder outside and an entrainment of foreign rnatter from outside, in addition, low temperature molding is impossible, and a molding fully satisfying the appearance, physical properties and another re~uirements has not been obtained.
Furthermore, for example, Japanese Unexamined Patent Publication (Kokai) No. 3-286811 discloses a thermoplastic elastomer molded article having an er~oss pattern, prepared by allowing a thermoplastic elastomer powder obtained by dynamically heat treating a mixture containing a crosslinking agent and polymer particles whlch comprise a crystalline olefin polymer portion and an amorphous olefin polymer portion and which have an avérage particle size of at least 10 ~m and an apparent bulk density of at least 0.2 g/ml to melt adhere to the internal surface of a mold for transferring an er~boss pattern to form grain patterns thereon and a method for produciny the same.
The method is similar to those described above, and TPO having a low flowability in the low shear rate region is allowed to melt adhere to the internal surface of the mold by spraying with a spray yun. Similar problems arise in the method, and moreover low temperature molding ~,, is impossible by the method. Sufficiently satisfactory molded articles have not been obtained yet.
In addition to the publications mentioned above, Japane~e Unexamined Patent Publication (Kokai) Nos. 4-10910, 4-10912, 4-16313, 4-21407, 4-2~408, etc., propose ,~

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powder molding of TPO. AS to the powders, these inventions are characteri~ed by using ~polymer particles comprising a crystalline ole~in polymer portion and an amorphous olefin polymer portion~ or ~a mixture comprising a polyolefin resin and an a-olefin copolymer rubber~'. The method for producing the molded articles of these inventions comprise ~placing these powders in metal molds for transferring an emboss pattern, heating the powders while the molds are being rotated to allow them to closely adhere to the internal surface of the molds in a fluidized plastic state and melt~ or ~allowing these powders to melt adhere to the internal surface of preheated molds for transferring an emboss pattern", in the presence of a crosslinking agent.
However, since these methods conduct molding and crosslinking reaction simultaneously, they have the following disadvantages: the molding cycle becomes long;
and the mold temperature must be raised in order to shorten the molding cycle. Moreover, there is also a ~isadvantage that gas sometimes evolves during the reaction, depending on the crosslinking agent to form ~inhole~ on the molded artlcle surface, Furthermore, low temperature moldlng ls lmpossible, and mol~ed articles having ~ufficlently ~atlsfactory appearances and physical propertiee have not been obtained yet.
SUMMARY OF THE I~n~TION
An object of the present invention is to ~olve the above problems, and provide a powder for powder molding comprising a thermoplastic resin or thermoplastic elastomer which has a hlgh flowability even when the mold temperature i~ low ana substantially no forming pressure ls applied, by which a molding having a required high thermal fusion strength between particles can be obtained without pinholes or a uniform section, and capable of being molded at lower temperature than the conventional powders to shorten ~he molding cycle and extend the mold ~' i~
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,, life, a powder molding method using the same and a molded article thereof.
Other objects and advantages of the present invention will be apparent from the following description.
1) In accordance with the present invention, there is provided a low temperature moldable powder for powder molding comprising a thermoplastic resin or thermoplastic elastomer composition, said resin or composition having a 0 complex dynamic viscosity ~* (170C) of 1.5 x 105 poise or less, as measured at an atmosphere temperature of 170C and a complex d~tamic viscosity ~* (250C) of 5.0 x 104 poise or less, as measured at an atmosphere temperature of 250C, in dynamic viscoelasticity measurements at a freguency of 1 radian/sec and a temperature average viscosity index k, calculated from the following formula, of 10 or less:
k = ~* (170C)/~* (250C) 2) In accordance with the present invention, there 2~ are also provlded a powder molding method, wherein the powder comprising the thermoplastic resin or thermoplastic elastomer composition as mentioned above i9 u~ed, and a molded article obtained thereby.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will be better understood from the description set forth below with reference to the accompanying drawings, wherein:
Fig. 1 is a plan view of a powder feed box of a powder slush molding device used in Examples;
Fig. 2 i8 an elevational view of a powder feed box of a powder slush molding device used in Examples;
Fig. 3 is a side elevational view of a powder feed box of a powder slush molding device used in Examples;
Fig. 4 is a plan view of a mold of a powder slush molding device used in Examples;
Fig. 5 is an elevational view of a mold of a powder slush molding device used in Examples;

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Fig. 6 is a side elevational view of a mold of a powder slush molding device used in the invention, and Eig. 7 is a graph showing the measurement results of viscoelasticities in Reference Examples 1 to 7 and Comparative Reference Examples 1 to 4.
DES~RIPTION OF THE PREFERRED EMBODIMENTS
The present invention will now be illustrated in detail hereinbelow.
According to the present invention, the characteristics of powder molding capable of giving molded articles having low residual strain and molding articles having a complicated configuration are utilized, and particularly automobile interior materials such as covering materials from a thermoplastic resin or thermoplastic elastomer excellent in lightweight, non-polluting properties can be provided.
Examples of the powder molding method of the invention include a powder rotary molding method or ~owder slush molding method Of these methods, the ~owder slush molding method is preferred. rrhe powder ~lush molding method refers to, for example, the molding method a~ clalmed in ~apanese Unexamined Patent Publication (Kokai) No. 58-132507.
Namely, the powder slush molding method comprises the ste~s of fixing a vessel having an opening and containing a necessary amount of a thermoplastic elastomer powder to a mold having an opening heated to a temperature sufficiently higher than the melting temperature of the thermoplastic elastomer powder, with the openings being matched to each other or fixing the vessel in the hollow portion of the mold to be integrated by quickly feeding the powder to the respective portions within the mold while the mold is rotated and/or rocked, to cause the powder to be melted and adhered thereto, and if necessary, discharging the superfluous powder into the vessel Specifically, for example, this is a method in which a mold with a surface temperature of 160C or higher and a vessel having an opening (a powder feeding box), which are integrated, are rotated or rocked to feed the thermoplastic resin or elastomer powder onto the inner surface of the mold through a natural flow, primarily due to the weight of the thermoplastic resin or elastomer powder (without spr~ying the powder onto the inner surface of the mold by a spray gun etc.), the resin or elastomer powder is melted and adhered to a uniform thickness by a thermal conduction from the mold, unadhered powder is recovered to the powder feeding box, the mold is separated from the powder feeding box, and thereafter, a thermal fusion of the melted and adhered powder is carried out under only the heat possessed by the mold or by an external application of heat followed by cooling and demolding to give a molding with a good appearance and mechanical strength.
The mold heating system to be used in the present invention includes the gas-fired furnace system, heated oil circulation system, dipping into a heated oil or a hot fluidized sand, and a high freguency induction heating system.
The thermoplastic resin or elastomer powder to be usea in this powder molding method must have a high powder flowability under a low shear rate and a low pressure, and be easily melted by the heat supplied primarily from the mold.
The specific feature of the present invention resides in a polypropylene or a propylene-a-olefin copolymer resin or in an elastomer composition comprising mixtures of ethylene-a-olefin copolymer rubbers and polyolefin resins, optionally dynamically partially crosslinked therewith in the presence of a crosslinking agent having a certain specific viscoelasticity, and in the use of a thermoplastic resin or elastomer powder obtained by powdering said resin or elastomer composition 1 o 2087661 at a lower temperature than the glass transition temperature. By the use of said thermoplastic resin or elastomer, it has become possible to carry out molding requiring a high flowability under a low shear rate such S as a powder rotary molding method and a powder slush molding method.
In the present invention, the thermoplastic resin or thermoplastic elastomer composition has a complex dynamic viscosity ~* (170C) of 1.5 x 105 poise or less, as 1 0 measured at an atmospheric temperature of 170C and a complex dynamic viscosity rl* (250C) of 5 . O x 104 poise or less, as measured at an atmospheric temperature of 250C, in dynamic viscoelasticity measurements at a frequency of 1 radian/sec. Preferably, ~* (170C) is 1 . 0 X 105 poise or less and ~* (250C) iS 3 .5 x 104 poise or less. More preferably, rl* (170C) is 3.0 x 104 poise or less and 71* (250C) iS 1.5 x 104 poise or less.
Particularly preferably, 1l* (170C) is 3.0 x 104 poise or less and 1l~ (250C) iS 4.5 X 103 poise or less.
2() When the complex dynamic viscosity ~* (170C), as measured at an atmospheric temperature of 17 0C is more than 1. 5 x 105 poise or the complex dynamic viscosity 1l*
(250C), as measured at an atmospheric temperature of 250C iS more than, 5 . 0 X 104 poise, the powder produced 2 5 from such a thermoplastic resin or thermoplastic elastomer composition comes not to melt on the mold at a temperature of less than 210C and cannot be molded by the powder moldiny method in which the shear rate during processing is as low as 1 sec-l or less.
3 0 Furthermore, in the present invention, the thermoplastic resin or thermoplastic elastomer composition has a temperature average viscosity index k of 10 or less, preferably 8 or less, calculated from the following formula by using the cornplex dynamic viscosity 3 5 1l* ~170C), as measured at an atmospheric ~emperature of 170C and the complex dynamic viscosity ~* (250C), as measured at an atmospheric temperaturic of 250C, in dynamic viscoelasticity measurements at a frequency of 1 radian/sec:
k = ~* (170C)/~* (250C) The thermoplastic resin or thermoplastic elastomer composition having a temperature average viscosity index k exceeding ten exhibits a marked temperature dependence of its complex dynamic viscosity even when it has a complex dynamic viscosity ~* (170C) of 1.5 x 105 poise or less as measured at an atmospheric temperature of 0 170C and a complex dynamic viscosity ~* (250C) of 5.0 x 104 poise or less as measured at an atmospheric temperature of 250C. AS a result, only molded articles having a nonuniform thickness can be produced due to the influence of the distribution or change of the mold IS temperature during processing.
In the present invention, preferably the elastomer composition is pulverized by the freezing pulverization method using liquid N2. Pellets of the thermoplastic resin or thermoplastic elastomer composition cooled to a pulverizing temperature of -40C or lower, preferably -70C or lower, more preferably -90C or lower, can be obtained by the mechanical pulverization method using a hammer mill, a pin mill etc.
If the composition is pulverized at a tem~erature higher than -40C, the particle sizes of the pulverized resin or elastomer powder are coarsened, and thus the powder moldability is undesirably lowered. To prevent an elevation of the polymer temperature to the glass transition temperature or higher during the pulverization operation, preferably a method having little heat generatio~ and a high pulverization efficiency is employed.
Also, preferably a pulverization apparatu~ which is cooled by an external cooling source is employed.
During the demolding of the powder molded product by an thermoplastic resin or an elastomer powder, the adhesion thereof to the inner mold surface is sometimes strong, and thus defects such as bending wrinkles or whitening may be generated when the demolding is forcibly attempted. Accordingly, it is often necessary before molding to coat the inner mold surface with a mold S release agent generally employed, such as dimethylpolysiloxane. For a continuous production of many moldings, however, the mold release agent must be coated for ever few moldings, which will lead to increased the costs. In such a case, although an improvement of the mold material is possible, the method of adding 2 parts by weight or less of a methylpolysiloxane compound as the internally added mold release agent per 100 parts by weight of the resin or elastomer composition, or the resin or elastomer powder 1S is effective. The addition in this case may be made either before or after the powdering. In this case, a methylpolysiloxane compound having a viscosity at 25C of 20 centistokes or more may be employed. The preferable viscosity range is 50 to 5000 centistokes; if the viscosity is too high, the effect of the mold release agent is reduced. On the other hand, if the amount of the internally added mold release agent is larger than 2 parts by welght, the thermal fusion between the resin or elastomer powder particles is inhibited and only a mol~ing having a low mechanical strength can be obtained.
Also, the internally added mold release agent bleeds out onto the mold surface, the mold is undesirably contaminated. Further, by controlling the amount of the internally added mold release agent,a reagglomeration after powdering can be reduced.
In the present invention, known heat-resistant stabilizers such as phenol type, sulfite type, phenylalkane type, phosphite type, amine type or amide type stabilizers, antioxidants, weathering resistant stabilizers, antistatic agents, metal soaps, lubricants auch as waxes, and pigments for coloration can be formulated in necessary amounts.

13 20 87 ~ 6 The molded articles according to the present invention can be applicable as products in the following various fields.
In the automobile fields, for example, various automobile parts including interior cover materials of, for example, instrument panels, console boxes, arm rests, head rests, door trims, rear panels, pillar trims, sunvisors, trunk room trims, trunk lid trims, air bag covers, seat buckles, head liners, gloves boxes and stearing wheel covers; interior molded articles of, for example, kicking plates and change level boots; exterior parts of, for example, spoilers, side moles, number plate housings, mirror housings, air dam skirt and mud guards;
and other molded articles of automobile parts.
In the electric home appliance and office automation device fields, housings and covering materials of the housings for, for example, television sets, video sets, washing machines, dryers, cleaners, coolers, air-condltioners, remote controller cases, electronic ovens, toasters, coffee makers, pots, thermoses, dish washers, electric razors, hair dryers, microphones, head phones, beauty appliances, compact disk cases, ca~sette tape cases, personal computers, typewriters, light projectors, telephones, copying machines, facsimile machines, telex machines, etc.
In the sport good fields, decorative parts of sport shoes, grips of rackets, sport tools and goods of various ball games, covering materials of saddles and handlebar grips of bicycles, motor-cycles and tricycles, etc.
In the housing and building fields, covering materials of furnitures, desks, chairs, etc.; covering materials of gates, doors, fences, etc.; wall decorative materials; covering materials of curtain walls; indoor flooring materials of kitchens, wash rooms, toilets, etc.; outdoor flooring materials such as verandas, terraces, balconies, carports, etc.; carpets such as 208~6:1 front door or entrance mats, table cloths, coasters, ash tray doilys.
In the industrial part field, grips and hoses for electric tools, etc., and the covering materials thereof;
packing materials.
In other fields, covering materials of bags, briefcases, cases, files, pocket books, albums, stationarys, camera bodies, dolls and the other toys, and molded articles such as watch bands, outer frames of picture or photograph and their covering materials.
EXAMPLES
The present invention will now be described in more detail with reference to the following examples, to which it is in no way limited. The dynamic viscoelasticity, powder properties and moldability of the thermoplastic resin or thermoplastic elastomer compositions, or the thermoplastic resin or thermoplastic elastomer powders, and the tensile properties of the molded sheets in Examples and Comparative Examples were determined by the following methods.
~ynamic viscoelasticity of re~in or elastomer ~QSit~l on~
The dynamic viscoelasticities at a vibration frequency of 1 radian/sec were measured at atmosphere temperatures of 170C and 250C in the parallel plate mode under the conditions of an applied strai~ of 5~ by using a dynamic analyzer Model RDS-7700 manufactured by Rhenometrics Co.
The tem~erature average viscosity index k was calculated according to the following formula, based on the results of ~* (170C) and ~* ~250C):
k = ~* (170C)/~* (2s0C) Powder flowability of resin or elastomer Dowders The resin or elastomer powder in an amount of 100 ml was charged to a funnel of a bulk specific gravity measuring device as specified in JIS (Japanese Industrial Standard) K-6721. The dumper was withdrawn, and the ~ime 1S 20876~1 (sec) from the start of the powder dropping until all the powder had dropped was measured.
The shorter the time, the better the powder flowability.
Preliminary evaluation of powder moldability of resin or elastomer ~owders (1) Powder Moldability An amount 500 g of the resin or elastomer powder was fed onto a nickel electroformed embossed plate having a size of 30 cm x 30 cm and a thickness of 3 mm, heated to a surface temperature of 170C, and adhered for 14 seconds, followed by a discharge of unadhered powder of said resin or elastomer powder, and the powder adhered on embossed plate was heated and melted in a heating furnace under an atmosphere temperature of 170C for 60 seconds.
The powder slush moldability was preliminary evaluated according to the following standards, from the fused state of the powder on the mold and the properties of the molde~ sheet obtained by demolding after water cooling the mold to 70C:
(o~: Sufficient mutual fusion among powder particles wa~ observed, and the resultant molded sheet had no pinholes;
O: Sufficient mutual fusion among powder particles was observed, and the resultant molded sheet had rarely pinholes;
~: Although mutual fusion among powder particles was observed, the resultant molded sheet markedly had pinholes; and X: Powder particles of the composition were not mutually fused, and remained as a powder on the mold.
C~ and O mean that the powder can be processed to give a final product, and A and X mean that a final product cannot be obtained by processing the powder.
(2) Demoldina force An amount 250 g of the resin or elastomer powder was feeded onto a nickel electroformed embossed plate having l6 2~87661 a size of 150 mm x 300 mm and a thickness of 3 mm, heated to a surface temperature of 170C, and adhered for 15 seconds, followed by a discharge of unadhered powder of said resin or elastomer powder, and the powder-adhered embossed plate was heated and melted in a heating furnace under an atmosphere temperature of 170C for 60 seconds.
Then, the mold temperature was cooled to 70C, at which a mold release was effected. This operation was repeated 10 times, and on the 10th mold release, the demolding force (peeling strength) between the molded sheet and the mold was measured by using a spring weighing scale. me best demoldability is exhibited at the smallest demolding force per width of 125 mm.
Phyc~ical Droperties of molded sheet The molded sheet obtained in the preliminary evaluation of the powder moldability test was punched to form a No. 1 dumbbel test sample as described in JIS K-6301, conditioned under the conditions of 23C, 50% RH for 24 hours, and then a tensile test was conducted under the ~ame corlditions by a tensile tester at a tensile speed of 200 mm/min. to measure the tensile strength at break and the elongation at break.

To 100 part~ by weight of a propylene-butene-1 random copolymer resin (butene-1 content = 24.4~ by weight, MFR = 2.2 g/10 min) was added 1.45 parts b~
weight of an organic peroxide (Perhexa~ 25B manufactured by Nippon Yushi K.K.~, and the mixture was subjected to a decomposition reaction at 220C by using a single screw 3~ extruder 65 mm in diameter to obtain resin pellets having a MFR of 1~0 y/10 min. The resin pellets were cooled to -100C with liquid nitrogen and then freeze pulverized to obtain a thermoplastic resin powder.
The powder moldability of the re~ultant po~der was preliminarily evaluated, and the results are listed in Table 1.
Reference Exam~le 2 17 20~766~

Resin pellets having a MFR of lO0 g/lO min was obtained in the same manner as in Reference Example 1 except that a propylene-ethylene random copolymer resin (ethylene content = 6~ by weight, MFR = lO g/lO min) was used as the thermoplastic resin and the amount of the organic peroxide was changed to l.lO parts by weight.
The resin pellets were then freeze pulverized under the same conditions as in Reference Example 1 to obtain a thermoplastic resin powder, 0 Reference ExamDle 3 A mixture of 45 parts by weight of an oil-extended EPDM (MLl+4 at 100C = 53) obtained by adding lO0 parts by weight of a mineral oil type softener (Diana Process~
PW~380 manufactured by Idemitsu Kosan Co., Ltd.) to 100 parts by weight of EPDM (MLl+4 at 100C = 242, propylene content = 28~ by weight, iodine value = 12), 55 parts by weight of the resin pellets obtained in Reference Example 1, 0.4 part by weight of a crosslinking coagent ~Sumifine~ ~M-bismaleimide compound manufactured by 2~ Sumitomo Chemical Co,, Ltd,) and 0,2 part by weight of a releasing agent ~SH~ 200, viscosity = 100 cSt, manufactured by Toray Silicone Co,, Ltd,) was kneaded by a Banbury mixer for 10 minutes and extruded to form a masterbatch ~referred to as "M.B,~ hereinafter) for crosslinking in a pellet form, To 100 parts by weight of the M,B, was added 0.04 part by weight of an organic peroxide (Sanperox~ AP0 manufactured by Sanken Chemical Co., Ltd.), and a dynamic crosslinking was carried out at 220C by using a twin screw extruder ~TEX~-44 manufactured by The Japan Steel Works, Ltd,) to obtain pellets of the elastomer c~m~osition, The pellets were freeze-pulveri~ed under the same conditions as in Reference Example 1 to obtain a thermoplastic elastomer powder.
~erence Exam~le 4 A thermoplastic elastomer powder was obtained in the same manner as in Reference Example 3 except that the oil-extended EPDM was used in an arnount of 40 parts by weight and 60 parts by weight of the resin pellets obtained in Reference Example 2 was used.
Reference Example 5 A thermoplastic elastomer powder was obtained in the same manner as in Reference Example 4 except that the oil-extended EPDM was used in an arnount of 36.4 parts by weight, that 54.5 parts by weight of th~ resin pellets and 9.1 parts by weight of a polyisobutylene (Tetrax~3T, viscosity average molecular weight=30000, manufactured by Nippon Petrochemicals Co., Ltd.) were used and that the organic peroxide (Sanperox~ APO manufactured by Sanken Chemical Co., Ltd.) was used for dynamic crosslinking in an amount of 0.12 part by weight.
Reference ExamDle 6 A thermoplastic elastomer powder was obtained in the same manner as in Reference Example 3 except that the oil-extended EPDM was used in an arnount of 30 parts by weight and 10 parts by weight of an ethylene-butene copolymer rubber (Tafmer~-4085 manufactured by Mitsui Petrochemical Industries, Ltd.) was further used.

A M.B. for crosslin~ing was obtained in the same manner as in Reference Example 3 except that the crosslinking coagent (Sumifine~ BM-bismaleimide compound manufactured by Surnitomo Chemical Co., Ltd.) was not added. A thermoplastic elastomer powder was obtained in the same manner as in Reference Example 3 except that 2 parts by weight of a mixture composed of 20% by weight of 1,3-bis(tert-butylperoxyisopropyl)benzene, 30~ by weight of divinylbenzene and 50% by weight of a paraffinic mineral oil was added as a crosslinkin~ agent.
Co~par~tive P.eference Exam~le 1 A thermoplastic resin powder was obtained by freeze pulverizing pellets of a propylene-ethyl*ne random copolymer resin (ethylene content = 6% by weight, MFR =

1.5 g/10 min) in the same manner as in Reference Example 1.
Comparative Reference Exam~le 2 A thermoplastic elastomer powder was obtained in the same manner as in Reference Example 4 except that the oil-extended EPDM was used in an amount of 70 parts by weight and 30 parts by weight of another propylene-ethylene random copolymer resin (ethylene content = 3%, MFR = 60 g/10 min) was used.
Comparative Reference Exam~le 3 Elastomer pellets were prepared in the same manner as in Reference Example 4 except that the oil extended EPDM in an amount of 50 parts by weight and an ethylene-propylene copolymer rubber (ML1+4 at 100C = 40, propylene content = 53% by weight) in an amount of 20 parts by weight (70 parts by weight in total) were used and that the propylene-ethylene copolymer resin employed in Comparative Reference Example 2 was used in an amount o~ 30 parts by weight. The resultant elastomer pellets were cooled to -80C and freeze pulverized to obtain a ther~loplastic powder.

A vinyl chloride resln (Sumilit~ SX 8G manufactured - by Sumitomo Chemlcal Co., Ltd.) obtained by conventional suspension polymerization was placed in a super mixer and stirred at a constant rotation rate while heated. When the resin reached a temperature of 80C, 70 parts by weight of a plasticizer (diisodecyl phthalate), 3 parts by weight of a thermal stabilizer (Ba/Zn type), 2 parts by weight of an epoxidized soybean oil, a pigment and a light stabilizer were added thereto, and the resulting mixture was dry blended. The resulting composition was cooled to a temperature of 50C or less when it reached a temperature of 120C, and a vinyl chloride resin (Sumilit~ PX-Q manufactured by Sumitomo Chemical Co., Ltd.) in fine particles was uniformly dispersed therein to obtain a thermoplastic resin powder.

ExamDle 1 A amount of 4 kg of the thermoplastic elastomer powder obtained in Reference Example 3 was thrown into a stainless steel s~uare vessel (i.e., a powder feeding box) 1 210 mm deep having a rectangular opening 2, 600 mm x 220 mm and being mounted on a monoaxial rotational device 4 as shown in Figs. 1 to 3. On the other hand, a nickel electroformed mold 5 ha~ing a 3 mm thickness as shown in Figs. 4 to 6, provided with an opening 6 having the same size as that of the opening 2 of the powder feeding box, having rope patterns 7 and leather emboss pattern 8 and shaped into a complicated configuration was preheated in a gas oven heated at 300C. Immediately after the surface temperature of the mold reached 170C, lS the heated mold was aligned with the opening 2 of the above-mentioned powder feeding box in such a manner that the opening 6, 600 mm x 220 mm, faced downward and an outer frame mounted around both openings was brought into close contact therewith, and the mold and box were then integrally flxed together by a clip 3. The assembly was lmme~lately clockwise rotated by two turns at 30 rpm and then counterclockwise rotated by two turns at 30 r~m.
Thereafter, the aeeembly wae clockwise shaken once through an angle of about 120 and counterclockwise ehaken once through an angle of about 120, to shake off excess ~owder adhering to the portion having a complicated configuration.
The rotation and shaking operation was stopped such that the opening 6 of the mold faced downward. The mold was then taken out of the powder feeding box, heated in a heating oven at 300C for 30 sec and cooled with water.
The molded sheet was then removed The resultant molded sheet 120 g in weight and 0.6 mm thick was free from underfill, and the rope pattern~
and the leather emboss pattern were exactly reproduced The molded ~heet was obtained as a pinhole-free product in which a minute portion of the mold having a 21 208766~

complicated configuration was sufficiently reproduced and which was excellent in even thickness.
A amount of 3.88 kg of the elastomer powder free from the inclusion of foreign matter was recovered in the vessel. An unused portion of the elastomer powder was added to the recovered elastomer powder, to a total weight of 4 kg, and the mixture was molded in the same manner as described above to obtain a product excellent in an appearance and an even thickness.
~
A molded sheet was demolded in the same manner as in Example 1 except that the thermoplastic elastomer powder obtained in Reference Example 4 was used and that the integrally fixed device was rotated through an angle of 180 at 30 rpm to become a state where the opening 6 of the mold faced upward, maintained in the state for 15 sec, and rotated through an angle of 180 in the same direction at the same rate to become a state where the opening 6 of the mold faced downward instead of rotating the integrally fixed device clockwise by two turns and counterclockwise by two turns at 30 rpm. The molded sheet could be easily removed, and the demoldability was good.
The resultant molded sheet 220 g in weight and 1.3 mm thick was free from underfill, and the rope patterns and the leather emboss pattern were exactly reproduced.
The molded sheet was obtained as a pinhole-free product in which a minute portion of the mold having a complicated configuration was sufficiently reproduced and which was excellent in even thickness.
Examnle 3 The procedure of Example 2 was repeated until the mold was taken out from the powder feeding box except that the integrally fixed device was maintained in the state of having been rotated throuyh 180 for 7 sec instead of 15 sec. The detached mold was allowed to stand to cool for 1 min at room temperature, and the molded sheet was demolded. The molded sheet could be easily removed, and the domoldability was good.
The resultant molded sheet 130 g in weight and 0.8 mm thick was free from underfill, and the rope patterns and the leather emboss pattern were exactly reproduced.
The molded sheet was obtained as a pinhole-free product in which a minute portion of the mold having a complicated configuration was sufficiently reproduced and which was excellent in even thickness.
Comparative ExamDle 1 The procedure of Example 1 was repeated except that the thermoplastic elastomer powder obtained in Comparative Reference Example 2 was used instead of the one obtained in Reference Example 3.
The powder particles fused together in the resulting molded article, but the fusion was insufficient. AS a result, the molded article was so brittle that the tensile strength could not be measured.
Com~arative ExamDle 2 The procedure of Example 2 was repeated except that the thermoplastic elastomer powder obtained in Comparative Reference Example 4 was used lnstead of the one obtained in Reference Example 4.
The powder particles fused together in the resulting molded article, but the fusion was insufficient. As a result, the molded article was so brittle that the tensile strength could not be measured.
The preliminary evaluation results of the powder moldability in Reference Examples 1 to 7 and Comparative Reference Examples 1 to 4 are shown in Tables 1 to 4 and Tables S to 6, respectively. Fig. 7 shows the dynamic viscoelasticity measurement results and the marks therein denote the follo~7ing results: ~ in Reference Exam~le l; +
in Reference Example 2; 0 in Reference Example 3; ~ in Reference Example g; ~ in Reference Example s; in Reference Example 6; x in Reference Example 7; ~ in Comparative Reference Example l; 0 in Comparative Reference Example 2; ~ in Comparative Reference Example 3; and ~ in Comparative Reference Example 4.
The physical properties of the molded articles obtained in Examples 1 to 3 are listed in Table 7.
s 24 20876~1 Table 1 Ref . Ex. 1 Ref . Ex . 2 nynami Vif~oel ~t; ; v of ~e~;n or ~ stomer ~ompo~;t;on rl* (170C) (poise) 6.6 x 103 5.2 x 103 ~* (2sOC) (poise) 9.5 x 1o2 1.3 x 103 1 0 Temp. Av. Viscosity Index k 6.95 4.00 Ptwfler Progert;es Powder Flowability (sec) 45 35 Powdt~r ~ol~abil;ty Powder Moldability O C) Demolding Force (kg/125 rnrn width) - -2 0 ~

Break Strength (kg/ctn2) 172 lB8 2 5 Break Elongation (%) 537 22 2s 2087661 Table 2 Ref.Ex. 3 Ref.Ex. 4 Dvnamic V;scoela~ti~;y of ~e~;n or ~la~tom~r Com~os;t;on ~* (170C) (poise) 1.2 x 104 7.0 x 103 :
~* (250C) (poise) 7.4 x 103 2.3 x 103 I O Temp. Av. viscosity Index k 1.62 3.04 Powfl~r ProDert ie~
Powder Flowability (sec) 15 19 ~f ~ V
Powder Moldability ~3 ~
Demolding Force (kg/125 mm width) 450 260 ~ M~lfl~ .~h~t Break ~trength (kg/cm2) 76 91 2 5 Break Elongation ~%) 504 ~65 2 6 2087~6~

Table 3 Ref.Ex. 5 Ref.EX. 6 Dynarnic Vi~c~ela~t;ciy f ~esin or El~omer rom~os;t;o~
~* (170C) (poise) 6.8 x 103 3.1 x 104 r~* (250C) (poise) 3.8 x 103 1.7 x 104 1 0 Ter~. AV. Viscosity Index k 1.80 1.82 ~wder Pro~ert;es Powder Flowability (sec) 30 29 ~l~r Mol d~h;l;ty Powder Moldability O O
~emoldirlg Force (kg/125 rnm width) 170 180 2 0 ~ ___ _ _ ~ __ _ ~r~r f M~
Break Strength (kg/cm2) 66 88 2 5 Break Elongation (%) 414 498 Table *

Ref . EX . 7 Dyn~m;~ V;~r~oela~t;o;y of Re~in or ~la~tomer Com~o~;t;on ~* (170C) (poise) 3.9 x 103 ~* (250C) (poise) 7.5 x 1o2 1 0 Temp. Av. Visco~ity Index k 5.20 Powder ~roperties Powder Flowability (sec) 26 Powder Mol dah;l;tv Powder Moldability O to Demolding Force (kg/325 mm width) 200 2 0 .~____ l Pr~er~
,L ShQe~
~reak C;trenc3~h (kc3/cm2) 111 2 5 Break Elongation (%) 556 Table 5 Co ~ .Ex~1 Comp.Ref. Ex . 2 Dy~m; V;~coelast;;y nf Re~;n or ~la~tomer comDo~;t;on (170C) (poise) 2.1 x 105 3.2 x 105 (2soC) (~oise) 6.7 x 104 1.3 x 105 0 ~emp. Av. Viscosity Index k 3.06 2.46 -Powder Prorert;e~
Powder Flowability (sec) 15 29 ,Powder Mol dahil~tv Powder Moldability X X
Demolding Force (kg/125 mm width) - -~-.-1 ol~ Mo1 defl Sheet Break Stren~th ~kg/cm2) 26 19 2 5 Break Elongation ~%) 5 23 Table 6 Comp.Ref.Ex.3 Comp.Ref. EX . 4 s Dynam;c V;~coPla~t;c;v of Re~;n or ~l~stomer co~o~;t;on ~* (170C) (poise) 3.9 x 105 1.8 x 105 ~* (250C) (poise) 1.5 x 105 1.0 x 103 1 0 . (at 220C) Ternp. Av. Viscosity Index k 2.53 2 180 Powder Pro~prt;es ] 5 Powder Flowability (sec) 63 13 P~wdPr ~ol dah;l;ty Powder ~oldability X X
2 0 ~ernol~ing Force (kg/125 mm width) - -Ph~LL~
~=~5 2 5 Break Strength (kg/cm2) ~r~ak Elongation (%) Table 7 Phys. Pro~erties of Molded Articles Break Strength Break Elongation (kg/cm2) (96) Ex. 1 88 520 Ex. 2 . 96 498 Ex. 3lL4 522 As described above, the present invention can provide a thermoplastic resin or thermoplastic elastomer powder for powder molding which resin or elastomer powder maintains a high flowability under the conditions of a low temperature atmosphere and almost no applied pressure for molding and from which a molded article having no plnholes and a sufficiently high thermally fused strength among ~owaer particles can be obtained by feeding the resin or elastomer powder on the internal surface of a mold without spraying by a spray gun, etc., a powder molding method using the same and a molded article thereof.

Claims (12)

1. A low temperature moldable powder for powder molding comprising a thermoplastic resin or thermoplastic elastomer composition, said resin or composition having a complex dynamic viscosity ?* (170°C) of 1.5 x 105 poise or less, as measured at an atmospheric temperature of 170°C and a complex dynamic viscosity ?* (250°C) of 5.0 x 104 poise or less, as measured at an atmospheric temperature of 250°C, in dynamic viscoelasticity measurements at a frequency of 1 radian/sec and a temperature average viscosity index k, calculated from the following formula, of 10 or less:
k = ?* (170°C)/?* (250°C)

2. A powder for powder molding as claimed in claim 1, wherein the thermoplastic resin is a polyolefin resin.

3. A powder for powder molding as claimed in claim 1, wherein the thermoplastic elastomer composition is an olefin thermoplastic elastomer composition.

4. A powder as claimed in claim 1, wherein the powder molding is powder slush molding.

5. A powder for powder molding as claimed in claim 1, wherein the molding temperature of the low temperature molding is less than 210°C.

6. A powder for powder molding as claimed in claim 1, wherein the powder comprises 100 parts by weight of the thermoplastic resin or thermoplastic elastomer composition as claimed in claim 1 and 2 parts by weight or less of a methylpolysiloxane compound.

7. A powder as claimed in claim 6, wherein the methylpolysiloxane compound is a dimethylpolysiloxane.

8. A powder molding method, wherein the powder as claimed in claim 1 is used.

9. A molding method as claimed in claim 8, wherein the powder molding method is a powder slush molding method.

10. A powder molding method as claimed in claim 8, wherein the molding temperature of the low temperature molding is less than 210°C.

11. A molded article produced by powder molding of the powder as claimed in claim 1.

12. A molded article as claimed in claim 11, wherein the powder molding is powder slush molding.