DE1720145A1 - Packaging method for unvulcanized rubber - Google Patents

Description

DR. MÜLLER-BORg DILPL.-lNG. GRALFS DR. MANITZ

PATENT LAWYERS

Braunschweig, May 11, 1967 Our reference: Bg / Be - P

Polymer Corporation Limited

oarnia, Ontario, Canada

Priority: Canada of Shark 13, 1967, No. 6613

Packaging process for unvulcanized rubber

The invention relates to methods of packaging unvulcanized rubber.

In the non-vulcanized state, rubber materials are solid, sticky masses that have a tendency to cold flow. This gives rise to problems for the manufacturer of synthetic rubber, who has to convey the freshly produced, vulcanized synthetic material to the rubber factories, where the rubber is to be vulcanized and processed into rubber articles. The unvulcanized rubber is conveniently delivered to the consumer in bales, the size of which is rjo [; ovjählb Ί :: t; allow C.

iii-O. '· "· .j ..'! I :: '), - :; L .ι /' ::. ·> .. 7, UIi ₁ I ..! L t; ■ 'Li ^c _j; Cr: t> o Vl i.'k I; ■ _ b ^ r.

109841/0394

that the bales lose their shape when left standing and during transport, if they are not held together. This makes the bales difficult to handle, especially when many bales are stacked on top of each other for transport. Furthermore, the tackiness of the Wk unvulcanized rubber is so great that it sticks to all common packaging materials such as sacks, paper bags, cardboard boxes or metal containers. The separation of the rubber from these materials after transport from the manufacturer to the consumer is extremely difficult. Individual balls of vulcanized rubber stick together firmly when they are brought into contact.

Several methods have been proposed, and have been used with varying degrees of success, to prevent this sticking and to ensure that the rubber maintains a convenient shape for the consumer after shipping. For example, it is common practice to dust the outer surfaces of the ball with talc; this helps prevent the rubber from sticking to paper, cardboard, etc., and usually does not have a particularly detrimental effect on the behavior of the rubber

109841/0394

BATH ORIGINAL

during subsequent processing. Dusting talc on a ball of rubber is an uncomfortable and dirty process. Also, the applied powder generally does not entirely prevent one unvulcanized rubber ball from sticking to another. The method is of no value in preventing the bales from deforming as a result of cold flow. Its usefulness ä ness is therefore on! Limited cases, where the bale individually packed in boxes or similar containers, but it is even there not always fully ivirksam.

Polyethylene films have recently been used as a wrapping material for unvulcanized rubber. you Use offers great advantages, but also throws Problems. Each transporting one wrapped in a foil With the rubber bale, the film cannot be separated from the rubber and the film must therefore be used with ™

are included in the entire subsequent processing of the rubber. Polyethylene is with rubber not compatible, especially not with types of rubber that have a high degree of polarity such as butadiene-styrene copolymers and butadiene-acrylonitrile copolymers. It is therefore essential that the polyethylene in the Rubber is completely dispersed so that it only acts as a filler. A complete dispersion

10 9 8 A1Λ039Α

but is in some. Cases hard to reach, especially when the blending of the raw polymer with the make-up additives is carried out at low temperature. In such cases lie in the completed Rubber items still discrete polyethylene beads in front of and lead to the presence of vulnerabilities in the article.

It is therefore desirable to keep the amount of polyethylene used as small as possible. This makes the use of thin foils appear advisable. For economic reasons, too, the foils should be kept as thin as possible. However, a certain minimum thickness of the film must be maintained so that the film has sufficient strength to keep the tendency of the rubber to cold flow within limits and to enable the bale to be handled during transport. It is not always possible to reconcile these two opposing demands. In addition, each good for coating of synthetic rubber used film strength properties must have at higher temperatures, because the bales are usually packed when they leave the baler and still have an elevated temperature of about 60 ⁰ C.

109841/0394

-. 5 -

The process for packing Rubber is characterized in that the rubber is coated with a film of a block copolymer a vinyl substituted aromatic compound and a conjugated diolefin is wrapped, the Block copolymers are compatible with the rubber, i.e. can form a homogeneous mixture with it.

According to a further feature of the invention, a pack of unvulcanized rubber with a foil encased a styrene-butadiene block copolymer, wherein the block copolymer has a molecular weight of 40,000 to 150,000, the film is translucent, one Thickness between 3.8 x 10 "^ and 12.7 x 10 ~ ^ cm (1.5 χ 10 "" ^ and 5 χ 10 "^ inches) and for Completion of the packaging is heat-sealed.

The invention offers particular advantages in the packaging of highly polar synthetic rubber materials such as butadiene-styrene copolymers, polybutadiene and butadiene-acrylonitrile copolymers. she is also used in the packaging of natural rubber.

The block copolymer films used in the present invention are made almost entirely of a polymer

109841/0394

Diolefins and a polymer of a vinyl-substituted aromatic compound, with the remaining Materials are small amounts of conventional additives for rubber, as described later should be added to the film at will during its manufacture, The description

While P of the invention relates specifically to styrene-butadiene block copolymers in the foils, but of course other chemically related diolefins can also be used except butadiene such as isoprene, piperylene, etc. and other vinyl aromatic compounds such as vinyl toluenes etc. can be used with good success. When wrapping of styrene-butadiene copolymer rubber according to the invention with a styrene-butadiene block copolymer film So the wrapping film, essentially from the

t materials from which rubber is made is what ensures compatibility of the materials., A rubber ball wrapped in this film can be used in the subsequent manufacture of articles can be used without removing the packaging film from the rubber must be separated. Even if the film is not completely in the rubber during mixing and processing is dispersed, the presence of discrete dips from the film has no adverse effect

109841/0394

on the rubber. The foil is with butadiene-acrylonitrile-Gopoiymeren also compatible, with the polybutadiene-polystyrene film is sufficiently similar in both chemical nature and polarity to ensure that the film is a ■ forms a completely homogeneous mixture with the rubber. It no discrete particles originating from the film can be seen in the mixed rubber. In case of Polybutadiene is not only compatible with other synthetic rubber materials, but also with the film ■ the presence of these small amounts of polystyrene from the Film can even be advantageous if the polybutadiene is then used to produce high-impact polystyrene should be used. The film shows the same excellent compatibility with natural rubber.

The packaging film generally contains a three homoblock copolymer of the general form polystyrene-polbutadiene-polystyrene. Such block copolymers are known to the person skilled in the art and can be prepared by anionic ones Polymerization of the first monomer in solution, addition of the second monomer to the solution after practically complete Polymerization of the first monomer and addition of the third monomer to the solution after practically more complete

109841/0394, ·

Polymerization of the second monomer. For the production of polystyrene-polybutadiene-polystyrene block copolymers So styrene is dispersed in a suitable hydrocarbon solvent and under the conditions the anionic polymerization polymerized with the aid of an initiator such as butyllithium. After complete polymerization of the styrene and without inactivating the polymer solution, butadiene will form the second polymer block added. If the butadiene is practically completely poly-P is merized, additional styrene is added to form the third block. As mentioned earlier, the block copolymer can also contain other related diolefins and other related vinyl aromatic compounds.

Apart from the three homoblock copolymers, the films can also consist of five, seven or even more homoblocks Contain polystyrene and polybutadiene, with the blocks in alternating order and each end- ™ permanent block is a polystyrene block, provided that the copolymers have satisfactory film-forming properties exhibit. Such multiblock copolymers can be obtained by repeating the "stepwise" addition of the anionic polymerization process described for triblock copolymers can be prepared until the required number of blocks has been "built".

109841/0394

But it can here and also in the case of the three-block copolymers alternatively, a difunctional initiator such as dilithiumhexyl can be used, so that an additional block at both ends of the already formed active polymer is polymerized with each addition of a further polymer.

As a further alternative, block copolymers can be used in which the middle block is a random (arbitrary) copolymer of butadiene and styrene, i.e. a block of the general form polystyrene (styrene-butadiene copolymer) -polystyrene is. Such block copolymers can be produced by a corresponding process as it was before in the manufacture of the three homoblock copolymers has been described, but the butadiene after only partial polymerization of the first Styrene charge added and the second styrene charge after complete polymerization of butadiene and the rest Styrene is added.

The production of films from these block copolymers can be made from solutions by a casting process. In this process, the block copolymer is used together with the respective additives that are added to the film should be dispersed in a suitable solvent such as toluene, being a fairly concentrated one

109841/0394

- «720145

- ίο -

viscous solution is obtained. This solution is then evenly spread out at room temperature by means of a bakel or a similar device on a sliding surface _f from which the film can be removed again (release surface) and the solvent is made to evaporate. The film is then peeled off the surface.

However, the foils can also be used according to one of the pour known as quenching and extrusion blowing Process are produced. In quenching roll casting, the polymer is fed into an extruder with an Archimedean mixer Brought screw training, where it is plasticized by the action of the screw. In the plastif In the icy state, the polymer is pressed by the screw through a narrow slot nozzle, from which it is shaped emerges from a thin film. The film has a temperature of around 120 ° C. when it emerges from the nozzle L is cooled by passing it through the gap formed between a pair of chilled rollers. At the Extrusion blow molding, the plasticized polymer is pressed by an Archimedean screw through a singing nozzle, the polymer normally moving in a perpendicular plane. Air gets through the inside of the The nozzle is blown in the direction of the polymer. The air flow serves to extrude the polymer into a thin one To stretch film.

109841/0394

Before the polymer is processed into the film, it is advisable to add a small amount of about 0.5 part by weight of a common antioxidant such as an alkylated bisphenol per 100 Mix in parts by weight of the polymer. In some cases it proved advisable to use the polymer to add an "antiblocking agent". A suitable antiblocking agent is diatomaceous earth, it is used in an amount of about one part by weight to 100 parts of the polymer

4 applied. "Blocking" is a property that affects the nature of the interface when the surfaces of two layers of film are pressed together. When the film "blocks", the two surfaces in contact appear as one, ie both together have approximately the same opacity as a layer of the film alone. This indicates that intimate contact has been made between the two surfaces, what. again shows that the two surfaces have a high resistance i to sliding on the intermediate surface

oppose -and have a tendency towards one another to adhere. For the purposes of the invention it is desirable that the film not "block" so that the in The foil wrapped rubber balls can easily be handled individually, even when they are stacked on top of one another are. Substances like diatomaceous earth and certain soaps and their derivatives can act as antiblocking agents on the polymer for the foil.

109841/0394

The block copolymer films are colorless, translucent, or transparent materials. They can be easily heat sealed for example with the help of a hot wire to complete the packaging of a rubber bale. In addition, their ink adhesion properties are good for certain common types of inks, which is a enables easy printability without special surface treatment. This is particularly desirable as it is often necessary to remove the individual rubber balls

fc to be identified by printing. Furthermore, these foils have w

a satisfactorily high tensile strength, suitable modulus and tear strength both at room temperature and at higher temperatures, at which the rubber bales are wrapped when they come out of the baler. ·

The block copolymers from which the films are produced expediently have a bonded content Styrene from 4-5 to 75 percent by weight and preferably from 55 to 65 percent by weight. In the case of three-block copolymers, where all of the terminal blocks contain a polystyrene block, these blocks preferably have approximately the same molecular weight. Block copolymers with too low a styrene content tend to have too little resistance to elongation (i.e., too low modulus) to the slope of a rubber ballena enough to suppress cold flow. Block copolymers with too high a styrene content it is easy to do something

1098 41 / 039A

brittle and hard and can therefore tear when handled. The Bloek copolymers suitably have a molecular weight of about 40,000 to 150,000 and, within these approximate limits, form films with good physical properties for use in the present invention. Since these films are compatible with the rubber materials for which they are used for packaging, it is not necessary for the thickness of the films to be kept to a minimum, which is advantageous in order to achieve a sufficiently high strength. Satisfactory films have a minimum thickness of about 2.5 x 10 cm (1 x 10 inches), and the best films are about 3.8 χ 10 "^ to about 6.4- χ 10 ~ ^ cm (1.5 x ΙΟ " ⁵ to 2.5 x 10" ⁵ inches).

In the case of incompatible films, it is essential that the temperature at which the rubber for whose packaging they are used is processed is considerably higher than the melting point of the film. Otherwise, only L takes place an insufficient dispersion of the film in the rubber, which the earlier disadvantages set entails. Therefore, such incompatible films as polyethylene cannot be used in cases where the rubber is processed at low temperatures of about 100 ° 0, which is the case, for example, when mixing on the roller, since this temperature is not sufficiently higher than the melting point of the Polyethylene film. Against it is

109841/0394

this problem "with the compatible Bloek copolymer films of the invention less acute.

The usefulness and advantages of the invention are presented based on described in the following examples:

Example I.

A three-block copolymer of the general form polystyrene-polybutadiene-polystyrene was produced which had a bound styrene content of 60 % and an intrinsic viscosity of 0.5 (corresponding to a molecular weight of about 52,000). The crude polymer had the following physical properties at room temperature

stocks:

Tensile strength 246 kg / cm ² (3,500 psi)

Elongation at break 570 %

100 % module 105 kg / cm ² (1500 psi)

300 % module ■ 13A- kg / cm ² (1900 psi)

Tear strength 25.5 kg / cm ² (360 psi) (Trouser tear strength)

To 230 grams of this polymer was added one gram of a powdered alkylated bisphenol as an antioxidant added. This finished polymer was dissolved in grams of toluene and a film was made from this solution poured.

1098 41/0394

For this purpose, the solution was made of a uniform thickness on a smooth, coated with a release agent Brushed surface. A knife was used for spreading out Gardner used, which was adjusted to a layer thickness of about 0.13 mm (0.005 inches). Of this The solvent became evenly layered Room temperature evaporated (which took about 15 minutes) and a clear sheet about a thickness Subtract 0.05 nua (0.002 inches) from the surface.

Small blocks of unvulcanized styrene-butadiene copolymer rubber measuring 5 σ 10 χ 2.5 cm (2 ^M χ A- " χ 1") were wrapped in this film. The foil was heat sealed around the blocks using a hot wire. Three blocks of the same rubber and size were also made but left unwrapped. The blocks were stacked in a cardboard box with the wrapped blocks on top of the unwrapped blocks. A 4 kg (9 pound) weight was then placed on top of the stack and placed in an oven held at 70 ° G. After storing under these conditions for 24 hours, the pack was removed from the oven and allowed to stand for four days at room temperature. Then the blocks were examined.

109841/0394

On removing the weight, it was found that the unwrapped blocks were inextricably stuck to the cardboard box. Sa $ had lost their original shape to a considerable extent and had partially "grown together". They could no longer be separated from each other.

The blocks wrapped in the block copolymer film, on the other hand, had retained their shape and did not stick the cardboard still together. This attempt mimicked, in a somewhat exaggerated manner, the conditions under which a rubber ball is exposed between production and consumption. The temperature of the oven was higher than it is likely to be expected for the bale in practice. In addition, the bales were open 24 hours maintained at this temperature, whereas in practice a bale is only kept at the maximum temperature for a few minutes will.

Example II

An experiment was carried out which served to determine the dispersion of the block copolymer film in the synthetic Watching rubber.

A sample of unvulcanized styrene-butadiene rubber was placed on a roller mill, the rollers of which were at 65 ° 0 were held. A roller head of the block copolymer, which corresponded exactly to that in Experiment I, but for the visual

1098 A1 / 0394

making a "blue dye" during the experiment was added to the rubber on the roller.

The temperature of the roller was then gradually increased and the temperature of the mixture was measured every two minutes.

The blue particles of the film could be seen as discrete spots. At a certain temperature, however, the discrete blue particles could no longer be observed and the entire mixture turned blue. This shows that the film was dispersed at this temperature in the rubber completely μ constantly. This dispersion temperature

was 106 ° G.

This experiment shows that the block copolymer film has a has a well-defined dispersion temperature, above which the film has a completely homogeneous mixture with the Rubber forms and becomes part of rubber in every way.

Example III ■

Another attempt was made to control the influence to determine the film in a mixed rubber, wherein the mixing temperature of the rubber is below the Dispersion temperature of the film was maintained.

A sample of unvulcanized styrene-butadiene rubber became a typical formulation for its manufacture

10 9841/0394

mixed in with tire treads, i.e. a mixture with Soot, a little oil, small amounts of suitable accelerators and antioxidants. This mixture was in one Banbury mixer manufactured. It then got out of the mixer taken out and cooled to room temperature. It was divided into two parts.

To either part was added about 1.5 parts of sulfur per 100 parts by weight of the mixture; the rubber was in a pouch made of the styrene-butadiene block copolymer film described in Example I. the The amount of film was about 0.2 percent by weight of the rubber, which is a greater proportion of film than normal is present when the film comes from the packaging of a rubber bale. The same amount of sulfur, however with no film portion, was added to the other portion of the mixture to make a control sample.

The two parts were then returned to the Banbury mixer separately and mixed for 4 minutes. It was care was taken that the temperature of the mixtures did not rise above 106 ° 0 (the dispersion temperature of the film determined in Example II). The two parts of the mixture were then drawn into rolled sheets, vulcanized by heating with sulfur and then vulcanized Condition checked for their physical properties.

109841/0394

In the physical properties investigated (tensile strength, consistency, modulus, tensile strength and hardness), no difference could be found between the part containing the undispersed block copolymer film and the control sample. This requirement means that the presence of iron undispersed film in the rubber that is not suitable for carrier wear does not have any negative effect on the rubber. It is therefore not essential that the mixing temperature of the rubber be higher than the bispersion temperature of the film when the rubber is wrapped in accordance with the invention.

109841/0394

Claims (3)

-20-1720U5 claims 1. A method of packaging unvulcanized rubber by wrapping the rubber in a thermoplastic Film, characterized in that the film is a block copolymer a vinyl substituted aromatic monomer such as styrene and a conjugated diolefinic ^ Monomers such as butadiene is used. 2. The method according to claim 1, characterized in that a film is used which is translucent and has a thickness of 3.81 χ 10 "" ^ ⁵ to 12.7 χ 1O ^- ^ cm. 3. The method according to claim 2, characterized in that that the block copolymer contains a small amount of an antiblocking agent was added. k 4 ·. Pack in the form of a wrapped in foil unvulcanized rubber, characterized in that that the film is a block copolymer of the general form polystyrene-polybutadiene-polystyrene with a Contains total molecular weight from 40,000 to 150,000. 1098 4 1/0394