CA1081383A

CA1081383A - Thermoplastic container for rubber chemicals

Info

Publication number: CA1081383A
Application number: CA265,714A
Authority: CA
Inventors: Allan R. Williams
Original assignee: UNIROYAL
Current assignee: UNIROYAL
Priority date: 1975-12-15
Filing date: 1976-11-16
Publication date: 1980-07-08
Also published as: AU504268B2; BE849402A; GB1544660A; FR2335334A1; NL7613808A; AU2054176A; BR7608388A; DE2656647A1; JPS5272743A

Abstract

Abstract of the Disclosure A film comprising thermoplastic resinous syndiotactic 1,2-polybutadiene is used to package rubber chemicals (including polymers). The package is added directly to a rubber batch being mixed, and is easily dispersed in the stock even at conventional final mixing temperatures.

Description

-` 108~3~33 This invention relates to a method of packaging an ingredient to be mixed into a rubber stoc~, and to a package containing such ingredient~ as well as to a - method of incorporating an ingredient in a rubber stock.
It has previously been common practiceto wrap or package rubber chemicals in a packaging material comprising low density polyethylene resin, to form a package which could be added directly to a rubber mi~, packaging material and all. Such prior practice has proven to be unfiatisfactory, in particular because of difficulty of obtaining satisfactory dispersion of the low density polyethylene packaging material in the final stage mixing of rubber stocks.
In accordance with the present invention, it has now been found that thermoplastic resinous syndiotactic 1,2-polybutadiene of controlled crystallinity having a low melting point can be used to form a package for rubber chemicals (including polymers) which can be added to a rubber mix, package and all, and is easily dispersed in the rubber stock at conventional final mixing temperatures.
The thermoplastic resinous syndiotactic 1,2-polybutadiene employed as a packaging material for ingredients to be added to a rubber in accordance with the invention usually has a crystallinity of from about 8 to about 35~, preferably about 22-28~, by weight, as measured by X-ray diffraction and density of the polymer. The polymer ordinarily has a crystalline melting point of from about 70 to 77C., perferably about 72 to 74C., and a glass transition point from :

10~13~3 about -14.5 to -29C., preferably about -17 to -21C., as measured by differential thermal analysis. The flow temperature of the polymer is typically about 90-110C., preferably 94-110C., measured in a capillary or on a melting bar. The intrinsic viscosity of this syndiotactic polymer is frequently about 0.9-2.5, preferably 1.0-1.8, deciliters per gram, measured in toluene at 30~C. It has a high permeability (to gases). Such a 1,2-poly-butadiene resin may be prepared for example as described in U.S. patents 3,498,963, Ichikawa et al., March 3, 1970, 3,522,332, Ichikawa et al., July 28, 1970 and 3,864,430, Umeno et al., February 4, 1975.
To use the described syndiotactic 1,2-poly-butadiene resin as a packaging material it is first converted into a film (or sheet) by a conventional technique for making thermoplastic films, such as by calendering or extrusion with or without subsequent orientation. Bags or similar containers or wrapping for rubber compounding ingredients (including poly-ZO mers) may be made from the film, for example by heat sealing.
The ingredients which may be prepackaged in this manner for addition to rubber stocks include the usual rubber chemicals or compounding ingredients such as accelerators, vulcanizing agents, activators, ~illers (e.g. carbon black, silica), polymers, pigments3 whether solids or liquids (provided of course that the physical properties of such liquids are not such as to permit them to swell~ dissolve or otherwise destroy the plastic packaging material) as in the case of some plasticizers - ~08 or extenders. The resulting package of pre-weighed com-pounding chemicals is serviceable and affo~s a convenient, clean and accurate way of preparing a rubber stock, by direct addition of the package to the rubber durlng the mixing operation, whether in an open mixer such as a roll mill or in an internal mixer such as a Banbury (trademark).
The present resinous packaging material melts low enough to be easily dispersed into rubber stock at conventional final mix temperatures, e.g., 180 to 210 or 220F.
The rubber to which the compounding ingredient, prepackaged in syndiotactic l,2-polybutadiene film in accordance with the invention~ may be added, may be any suitable conventional rubber, whether natural or synthetic, as exemplified by such unsaturated vulcanizable rubbers as the con~ugated diene polymers, whether homopolymers as in cis-polybutadlene, cis-polyisoprene (natural or synthetic), or copolymers as in butadlene-styrene, butadiene-acrylonitrile, butadiene-vinyl-pryridine, and l isobutylene-isoprene copolymer rubbers. Another example - 20 of a suitable rubber stock is that of the monoolefin copolymer rubber type, as represented by the ethylene-propylene-noncon~ugated diene terpolymers known as EPDM.
The method of the invention is adaptable to use with mechanized or automated pre-weighing systems and insures accuracy and reproducibility with a minimum occasion for direct contact between an operator and the rubber chemical. Use of packaged chemicals ensures cleanliness (no powders blowing around), accuracy (no hold-up in a dumped container), and speed (the mixer attendant does not have to weigh up chemicals for each 108~3~3 batch).
The following example~ will serve to illustrate the practice of the invention in more detail Example 1 Thermoplastic syndiotactic 1,2-polybutadiene resin ("1,2-PBD") manufactured by Japan Synthetic Rubber Company~ grade RB 820, is used in this example.
This material has an intrinsic viscosity of 1.27 decil~ters per gram, measured in toluene at 30~C., a crystallinity of 24.5% by weight, and a melt index of 1.98 measured at 150C. and 2,160 g.load.
The resin is converted into a film by extrusion in a 1-1/2 inch Davis-Standard Thermatic (trademark) extruder in which all heating zones were at 330F.;
the cooling and polishing rolls (three in number) were at 75F ; the die dimensions were 12 inches by 0.012 inch. Draw ratio at the windup was about plus 50~.
The fi~ produced was about 10 mils thick and had the following properties, compared to a low density poly-ethylene (LDPE) film:
1~2-PBD LDPE
Softening point (Vicat) 60C. 850C.
Heat-seal temp 75-80C. ~100C.
"Heat-seal temp." is measured by applying a heated metal bar briefly to two sheets of the thermoplastic film on a thermally insulated surface. "Vicat so~en-ing pt " is measured according to ASTM D1525.
To e~aluate the films, a 2.75-inch roll laboratory mill may be loaded with approximately 100 grams of approximately 48 Mooney (ML-4-212F.) carcass 108~3~3 stock ~e.g., lOO parts of a blend of SBR, cis-1,4-polybutadiene and natural rubber in approximately equal proportions, ll parts naphthenic oil, 40 parts carbon black, 4 parts zinc oxide, 3 parts stearic acid,

2 parts acetone-diphenylamine condensation product [antioxidant], l part disproportionated rosin~ 4 parts sulfur, and 2. 5 parts N-cyclohexyl-2-benzothiazole sulfenamide [accelerator]). The nip is set to establish a 1/8 inch thick band and an active bank. 3/4 inch by 4 inch strips of 5-mil LM E film and 10-mil 1,2-PBD
were compared by observing their behavior when intro-duced directly into the bite, m e observations made in four different experiments are listed in Table I, below. No cutting of the band was employed except as noted in Experiment 4.

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It is concluded from the tabulated experiments that 1~2-PBD offers a 15 to 30F. safety factor compared to LDPE. The new resin packaging material of the in-vention not only melts lower but is more compatible with rubber stocks than LDPE ~note that stock ~t 150F. does not band coherently on a roll mill). In addition, it has the added virtue of being easily co-vulcanized with the polymers in a rubber stock once it has been dispersed into the stock.
; 10 Example 2 mis example illustrates the preparation of small bags from 1,2-PBD film and use of them for adding final cure chemicals to a second stage rubber mix.
Sheets 10 inches square may be cut from a calen-dered film of 1,2-polybutadiene resin described in Ex-ample 1. To make a bag two sheets are superimposed one upon the other and heat sealed along three sides by contacting with a metal bar heated to 75-80C., thus providing an open-ended pouch. 4.32 pounds of sul~ur and 2.47 pounds of N-cyclohexyl-2-benzothiazole sulfen-amide (accelerator) are weighed separately into two such pouches and the open ends are heat sealed as described above to close the bags. Into a No. 11 Banbury are charged 400 pounds of a masterbach, mixed in the proportions of 100 pounds of SBR, 50 pounds of high abrasion furn~nce black, 4 pounds of zinc oxide, 3 pounds of stearic acid, 1 pound of N,N'-diphenyl-p-phenylenediamine, 1 pound of disproportionated rosin and ~ 3 pounds of pine tar, followed by the two pouches of - 30 sulfur and accelerator. Within two minutes the pouches iO81383 and their contained chemicals will have become incorporated into the batch, and the batch can be discharg~d to the drop mill ~or conventional blending. Additional process- ;
ing and eventual vulcanization can be carried out in normal fashion.

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Claims

What is claimed is;

1. A method of packaging an ingredient to be added to a rubber stock during mixing of the said rubber stock comprising enclosing the said ingredient in a film of thermoplastic resinous syndiotactic 1,2-polybutadiene as a packaging material to form a package of said ingredient in the said film, whereby, when the resulting package is added to a rubber stock and mixed therewith at elevated rubber stock mixing temperature, the film of thermoplastic resinous syndiotactic 1,2-polybutadiene packaging material becomes incorporated uniformly into the rubber stock within a short mixing time, the said thermoplastic resinous syndiotactic 1,2-polybutadiene having the following characteristics:

2. A method as in claim 1 in which the said thermoplastic resinous syndiotactic 1,2-polybutadiene has the following characteristics:

3. A packaged ingredient to be added to a rubber stock during mixing of said stock comprising the said ingredient enclosed in a film of thermoplastic resinous syndiotactic 1,2-polybutadiene as a packaging material to form a package of said ingredient in the said film, the said package being characterized by the fact that the film of thermoplastic resinous syndiotactic 1,2-polybutadiene packaging material becomes incorporated uniformly into the rubber stock within a short mixing time when the package is added to a rubber stock and mixed therewith at elevated rubber stock mixing tempera-ture, the said thermoplastic resinous syndiotactic 1,2-polybutadiene having the following characteristics:

4. A packaged ingredient as in claim 3 in which the said thermoplastic resinous syndiotactic 1,2-poly-butadiene has the following characteristics:

5. A method of incorporating an ingredient in a rubber stock during mixing of the said rubber stock comprising enclosing the said ingredient in a film of thermoplastic resinous syndiotactic l,2-polybutadiene as a packaging material to form a package of the said ingredient in the said film, and thereafter adding the resulting package to a rubber stock and mixing the package and rubber stock together at elevated rubber stock mixing temperature whereby the film of thermo-plastic resinous syndiotactic 1,2-polybutadiene packaging material becomes incorporated uniformly into the rubber stock within a short mixing time, the said thermoplastic resinous syndiotactic l,2-polybutadiene having the following characteristics:

6. A method as in claim 5 in which the said thermoplastic resinous syndiotactic l,2-polybutadiene has the following characteristics:

7. A method as in claim 6 in which the said mixing temperature is from 180 to 220°F.

8. A method as in claim 7 in which the said rubber stock is a conjugated diene polymer rubber stock.

9. A method as in claim 8 in which the packaged ingredient is sulfur.

10. A method as in claim 8 in which the packaged ingredient is an accelerator of sulfur vulcanization.