Improved Process for Producing Customized Thermoplastic Resins
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s\ — IIIIIMIIIIIIIIIIIIIIIIIIIII OJII Eur°Pean Patent Office <*S Office europeen des brevets (11) EP 0 889 075 A1 (12) EUROPEAN PATENT APPLICATION (43) Date of publication: (51) int. CI.6: C08J 3/22 07.01.1999 Bulletin 1999/01 (21) Application number: 98110777.4 (22) Date of filing: 12.06.1998 (84) Designated Contracting States: • Brian, Bernd B. AT BE CH CY DE DK ES Fl FR GB GR IE IT LI LU Plymouth, Michigan 48170 (US) MC NL PT SE • Tuttle, Mary E. Designated Extension States: Trenton, Michigan 48183 (US) AL LT LV MK RO SI • Popovski, Blagojce Warren, Michigan 48092 (US) (30) Priority: 30.06.1997 US 884891 (74) Representative: (71 ) Applicant: BASF CORPORATION Schmitz, Martina Rosemarie et al Mount Olive, New Jersey 07828-1 234 (US) BASF Aktiengesellschaft Patentabteilung ZDX/A - C6 (72) Inventors: 67056 Ludwigshafen (DE) • Hurley, James M. Grosselle, Ml 48138 (US) (54) Improved process for producing customized thermoplastic resins (57) Disclosed is a customized thermoplastic resin having a thermoplastic resin body and a coating on the thermoplastic resin body. The coating contains a hydro- phobic resin component and at least one additive. The hydrophobic resin component of the coating has an onset temperature for its melt processing range below the onset temperature for the melt processing range of the thermoplastic resin body. The customized thermo- plastic resins of the invention may be produced more efficiently than conventional customized thermoplastic resins, while the customized thermoplastic resins of the invention may be used in the same methods as conven- tional materials to produce many useful articles. < LO o <7> CO CO o Q_ LU Printed by Xerox (UK) Business Services 2.16.5/3.4 1 EP 0 889 075 A1 2 Description the manufacturing costs of the specialized product. Alternatively, colored articles have been produced The present invention relates to colored thermo- by dry blending the uncolored thermoplastic resin with a plastic resins that are useful for molding articles. In par- color concentrate (also known as color masterbatch) in ticular, the invention relates to customized s what is known in the art as a "salt and pepper blend." thermoplastic resins that have a thermoplastic resin The thermoplastic resin and the color concentrate used body, or base resin, coated with a layer of a lower melt- for such blends are typically of similar size pellets or ing second thermoplastic composition. The second pieces. The color concentrate is usually a minor amount thermoplastic composition comprises at least one addi- by weight of the blend, typically only up to about 5% by tive, preferably a colorant or pigment, and particularly w weight, and often much less. The salt and pepper blend preferably an additive not present in the first thermo- is then introduced directly to the molding or forming plastic composition. In a preferred embodiment, the equipment used to produce the final article. The melt second thermoplastic composition contains as an addi- blending of the uncolored resin and the color concen- tive a dispersed pigment. The thermoplastic resin com- trate must take place in the molding or forming equip- posite is formed into an article by melting and mixing is ment. This process, however, can result in color together the first and second thermoplastic composi- variations from piece to piece, or even in areas within tions and extruding, molding, or otherwise shaping the the same piece, because of incomplete blending, partic- blend into the article. ularly for low blending ratios of the color concentrate. Thermoplastic resins are formed into many kinds of Segregation of particular additives during packaging articles, for example by extrusion, thermoforming, and 20 and transportation may also be experienced with dry compression molding processes. The thermoplastic blends and contribute to lack of homogeneity in the final resins are usually compounded and manufactured as formed articles. pellets or powders that may be easily shipped and that In a method related to the use of a salt and pepper may be easily and conveniently handled during forma- blend, lakes and liquid colors can be introduced at the tion of the desired articles or stored for later processing. 25 mouth of an injection molding extruder or into other It is most economical to manufacture the thermoplastic forming equipment. This method also has a number of resins as pellets in a continuous extrusion process in drawbacks. In the first place, sophisticated metering which the pellets are compounded to meet the require- equipment may be required by the fabricator in order to ments of many uses. produce uniform coloration. In the second place, this It is often the case, however, that a thermoplastic 30 method is similar to the salt and pepper method in that resin must be specially formulated or customized for a the coloring material and the uncolored resin are intro- particular use or application, such as mold-in color proc- duced essentially separately, relying on a thorough mix- esses, for example by including special additives for that ing in the forming equipment before the article is finally use, such as pigments to achieve a particular color or a shaped. Incomplete blending and color variations can stabilizer package that meets the requirements of a par- 35 easily result. ticular use. In particular, thermoplastic resins may be Gose et al., in U.S. Pat. No. 5,443,910 and related customized to include certain pigments and/or color- patents, describe applying certain processing, stabiliz- ants. It is often desirable that the manufactured article ing, or other functional polymer additives to polymeric have a particular color. A particular color may, for exam- particles by spraying the particles with an aqueous ple, enhance aesthetic appeal of the article or may even 40 emulsion of the polymer additive. The emulsion includes serve to help identify the particular brand or manufac- an emulsifiable (acid-functional) wax, surfactant, a turer. base, the additive, and the water. This method of cus- Customizing the color or additive package of ther- tomizing thermoplastic resins, however, has several moplastic resins can, however, present problems. While drawbacks..First, the inclusion of a base compound in the general purpose thermoplastic resin, or base resin, 45 the applied material may cause unwanted coloration or may be produced by continuous extrusion operations, color shifts. For example, Gose et al. note a problems colored thermoplastic resins or thermoplastic resins when potassium hydroxide or sodium hydroxide is used. with special additive packages are typically required in It is also well-known that discoloration may result from much smaller amounts that are relatively expensive to amines in certain systems. Secondly, the water of the produce..Manufacture, especially post-production so emulsion, or the combination of water and base, cleaning, is extremely labor instensive. The processing present problems for hydrophilic resins. In addition, it equipment (such as blenders, feeders, extruders, and may be desirable in some instances to exclude sur- pelletizing equipment) must be thoroughly cleaned after factants from the thermoplastic resin. Finally, the emul- each particular color or customized blend in order to sion application method has drawbacks that are avoid contamination of the thermoplastic resins that will ss inherent in the process, for instance, that the applied next be produced in the equipment. The cleaning proc- layer of emulsion must be dried and the emulsion must ess requires significant down time of the equipment dur- be stored and used under carefully maintained condi- ing which no material is being manufactured, adding to tions to prevent destabilization and separation. 2 3 EP 0 889 075 A1 4 Sharma, in U.S Pat. No. 5,300,256 and related pat- one may employ the difference of the highest, lowest, or ents, also describes applying an additive to a polymeric average temperature within a range; the term preferably particle from an aqueous medium. Sharma discusses emplys the most meaningful separation of temperature the handling and storage problems of the Gose and pro- in the application under consideration. vides a solid additive system that can be dispersed in 5 In a preferred embodiment, the coating comprising water just prior to application. The polymer additives the hydrophobic resin component and at least one addi- used by Sharma must melt at a temperature no higher tive is a color concentrate. In a process for producing than 100°C, and may include hydrophilic polymers such the customized thermoplastic resins of the invention, as low molecular weight polyolef ins with carboxylic moi- the thermoplastic resin body is contacted with the coat- eties. The additives again contain water and are further w ing at a temperature at which the hydrophobic resin diluted with water and applied as an aqueous emulsion, component is a melt. The coated resin pieces are still with many of the attendant problems as mentioned cooled to solidify the coating in a layer on the thermo- above. plastic resin body or piece. In a preferred embodiment, It is also known to prepare color concentrates by a a substantially even thickness of an outer layer of the method of blending together a mixture of pigment, low is customizing hydrophobic resin component is applied. molecular weight polyethylene wax, and thermoplastic The coated resin pieces or pellets are easy to handle polyolef in granules. The pigment and wax is included at and may be formed into articles using the same proc- relatively high levels, for example approximately 40% by esses and in the same way as would resin pellets that weight of the mixture. The wax dispersed the pigment have had the color or other additive integrally mixed in. forms a layer on the polymer granules. This master- 20 The color concentrate or other customizing coating batch is blended with unmodified base polyolefins to composition is coated onto the resin after the resin form a "salt and pepper8 blend.