DE2242704B2 - Ethylene copolymer tablets of reduced stickiness - Google Patents

Description

The invention relates to tablets made from ethylene copolymers of reduced stickiness.

The previous measures to reduce the stickiness of Polymei sattabletten largely existed in dusting with a powder as a release agent. For this purpose you have powder, like Talc and silica are used. However, these substances have the disadvantage that the coating is chemical Properties of the polymer changes. For most purposes, the polymer is in its purest possible form.

U.S. Patent 3,528,841 relates to the use of microfine polyolefin powder coatings, in order to cause the least possible change in the overall properties of the polymer, because (1) the amount of coatings then only needs to be 0.025 percent by weight and (2) very small Particles distribute themselves well when the tablets are used for their end use.

British Patent 1113,348 relates to a Another method in which a dispersion of a sticky elastomer, such as a copolymer from Ethylene and vinyl acetate of high vinyl acetate, polybutadiene, etc. coagulated and then one Dispersion of a hard polymer, such as polyvinyl chloride, polystyrene, pol) methacrylic acid methyl ester, coagulated onto the coagulate of the sticky polymer whereupon a non-sticky powder is obtained after washing and drying. This However, coagulation process leads to the formation of a rough outer layer with poor abrasion resistance, and therefore, the improvement in handling obtained by reducing tackiness can be achieved easily lost again. Furthermore, coagulation is an ineffective coating method because a considerably larger accumulation of the second coagulate is required in order to achieve an improvement to achieve caking.

The invention provides ethylene copolymer tablets of reduced stickiness available in the essentially consisting of an ethylene copolymer core with a macroscopically smooth, permanent coating in the form of a partially fused film made of a harder, less sticky type of ethylene copolymer exist.

The invention includes; also a method for Reduction of the stickiness of tablets made from ethylene copolymers by coating the tablets with a harder, less sticky type of ethylene copolymer, e.g. B. by immersion in or Spraying with a dispersion or solution of the harder type of copolymer, and then Dry.

In the context of the present description, "tablets" are spherical, cylindrical or even slightly less symmetrical shapes with diameters of about 1.6 to 6.35 mm. The critical limitation in the size of the tablets to be coated is the amount of

, ο coating appropriate for the application in question

is permitted (e.g. assign tablets with very small Cores have a larger percentage of plating on) -

If you have copolymer tablets made from ethylene

and vinyl acetate with a harder, less tacky type of copolymer of ethylene and vinyl acetate Coated, it has been shown that the stickiness of the tablets is thereby substantially reduced and significantly improves their maneuverability in manufacture as well as in end use. Of the coating thus leads to a reduction in manufacturing costs and to a better handling by the customer, which increases the value of the product. The harder, less sticky type of copolymer can, for. B. obtained by a copolymer chooses the one that has a lower vinyl acetate content, a higher molecular weight, or both having.

The invention is particularly suitable for reducing the stickiness of tablets made from copolymers from ethylene and vinyl acetate and the corresponding terpolymers with methacrylic acid, however, it can also be used for other ethylene copolymers. So you can use as ethylene copolymers for the tablet core and / or for the coating

z. B. copolymers of ethylene and vinyl esters, such as ethylene and vinyl acetate, and the corresponding Terpolymers with acidic monomers, such as acrylic acid and methacrylic acid, and with carbon monoxide, such as copolymers of ethylene, vinyl acetate and carbon monoxide, copolymers from Ethylene and acrylic or methacrylic acid esters, such as copolymers of ethylene and acrylic acid isobutyl ester, as well as the corresponding terpolymers with acidic monomers, such as acrylic acid and methacrylic acid, binary copolymers of ethylene with acidic monomers, such as acrylic acid or methacrylic acid, binary copolymers and terpolymers of ethylene and monomeric olefins, such as copolymers made of ethylene, propylene and hexadiene.

The copolymers of ethylene, vinyl acetate and carbon monoxide that can be used are those those described in U.S. Patent Application Serial No. 169,792, filed Aug. 6, 1971.

The coating made from the harder type of copolymer can expediently be applied by the sticky tablets are coated with liquid dispersions or solutions of the harder type of copolymer and then let it dry.

The amount of coating applied is not critical; however, the coating should preferably about 0.01 to 5 percent by weight of the coated tablet.

Although the invention is of more general applicability, it is detailed below under Reference to the reduction of the stickiness of copolymer tablets made from ethylene and vinyl acetate by covering them with a dis-

persion of a harder type of the same copolymer described.

The invention is particularly suitable for reducing the stickiness of ethylene-vinyl acetate copolymer tablets, in which the product from the vinyl acetate content (expressed in percent by weight) and the logarithm of the melt index is at least about 40.

There are several types of aqueous dispersions that are used to reduce the tackiness of copolymers Ethylene and vinyl acetate can be used, commercially available. The making of this Dispersions is described in U.S. Patent 3,347,811 which are incorporated herein by reference. The stable dispersions can either be a sodium salt of dimerized rosin or sodium lauryl sulfate as a surfactant and also small amounts Contains wax to further increase the hardness of the mass. The mean particle size in these systems is typically 0.6 μ .. The extent of the reduction observed in the sticky polymer tablets the tack depends on the particular polymer and the composition the dispersion.

After choosing the right dispersion, the sticky tablets are placed in the aqueous dispersion (the z. B. 5 to 50 weight percent solids), preferably at room temperature. After a short time Immersion, e.g. B. after one minute, the tablets are removed from the dispersion and air dried. The dried tablets have a macroscopically smooth, permanent coating in the form of a partially fused film. "Permanently" means that the coated tablets in pneumatic conveying systems are resistant to abrasion and are easy to use can be handled without significant loss of coating.

Elevated temperatures should be avoided, otherwise the tablets and the coating become stickier has a tendency to clump together in individual places. Higher temperatures would also favors the migration of the coating into the tablets, thereby increasing the degree of improvement in terms of the stickiness would be reduced. This hike only takes place at room temperature extremely slowly.

The reduced stickiness of the copolymer tablets according to the invention is of particular advantage in the continuous production process of ethylene copolymer tablets.

Such a continuous high-pressure radical chain polymerization process is typically carried out as follows: (a) The reactor is charged with ethylene and at least one other monomer selected from the group of vinyl esters of monobasic aliphatic C ₁ - to C ₄ carboxylic acids, acrylic and methacrylic esters Alcohol radical is derived from aliphatic monohydric C ₁ - to C ₄ alcohols, acrylic acid, methacrylic acid, maleic acid and maleic anhydride is selected, provided that the monomers consist of at least 85 mole percent ethylene and an initiator for the reaction; (b) maintaining the monomer and the initiator in the reactor at temperatures of about 100 to 250 ⁰ C and pressures of about 1000 to 2500 at contact with each other until it reaches the desired degree of conversion to Äthylencopolymerisaten; (c) removing the reaction mixture from the reactor; (d) the pressure is reduced in one or more stages; (e) Virtually all of the unreacted monomers are separated from the reaction mixture, and (f) the ethylene copolymer is introduced into a melt cutting device, where it is pressed through an extrusion orifice and thereby cut into tablets under water. For easy handling after

ίο which should be extruded, cut and dried the tablets are pneumatically conveyed from the dryer to cleaning mixers. In these big ones The remaining vinyl acetate is removed from the tablets using one of the storage containers driven down upward penetrating air flow. Also, the tablets are made at the same time mixed by the air flow by being withdrawn from different points of the container space and be returned to the head of the container. Adhesive

Some, not free-flowing tablets are suitable * for a no such treatment, because in this case the contents of the container cakes together to form a large mass. Therefore, after drying, such tablets must be placed in large boxes and treated pneumatically by inserting a pipe through the bottom of the box. You can then go into this Boxes can be sold as a block, or they can be broken apart with difficulty and filled into bags. Non-sticky tablets, on the other hand, can be pneumatically added to the Convey storage containers and from there to the packing station, where they are automatically packed in bags will.

The dispersion of the harder, less sticky type of ethylene copolymer can be applied from the water which is used to make the tablets after extrusion of the present in bulk Resin to cool when cutting. Preferably the tablets can e.g. B. to the coating to allow a lower tablet temperature to immerse in the dispersion after cutting. Another method can be used to spray the dispersion onto the tablets. In both cases the dried tablets have sufficiently low tack to stand in normal bulk processing equipment to be handled.

In the following examples, parts and percentages are used unless otherwise specified refer to the weight, the following abbreviations for the copolymers of ethylene and vinyl acetate used:

description
of the copoly- Vinyl acetate
salary Melt index Shore A hardness *) mcri sats Weight percent g / 10 min A. 28 6th 80 B. 40 55 35 C. 25th 2 85 D. 33 24 67 E. 18th 2.5 88 F. 28 150 67 G 28 25th 72

*) The hardness is measured with the Shore A 2 durometer with a test duration of 10 seconds in accordance with the ASTM test standard D-1706 determined.

example 1

A solution of 5 g of copolymer A in 100 ml of toluene is prepared. Several grams of tablets the copolymer B are briefly immersed in this solution. Then air-dried Tablets are slightly less sticky, while those that are dipped in acetone are used to make the coating to fail, and then to be dried, are considerably less sticky. At concentrations of At 1 g / 100 ml the tablets are still sticky, and at concentrations of 10 g / 100 ml or more they are Solutions too viscous to run off and you do not get properly coated tablets.

Example 2

20 tablets of copolymer B are mixed in the following mixtures from a dispersion of the copolymer C with a solids content of 50% and immersed in water. Then the tablets are sent to the Air dried on polyethylene terephthalate film.

Table I.

No. Disper
sion H ₂ O Copolymer C Dried tablets ml ml % 1 50 0 50 free flowing 2 10 40 10 free flowing 3 2 48 2 less sticky
as copolymers
sat B, but not
free flowing 4th 1 49 1 less sticky
as copolymers
sat B, but not
free flowing 5 0 50 0 just as sticky
like copolymers
sat B and not
free flowing 6th 0 30th 0 + 1 trop
30%
Sodium-
lauryl sulfate just as sticky,
like copolymers
sat B and not
free flowing

In another experiment, 100 tablets made of copolymer B, which are still sticking together, are closed added to the above dispersions No. 2 and 3, respectively. It is found that with only slight stirring the No more caking tablets. If the tablets are stirred in pure water (see No. 5), keep baking. With the addition of surfactant (No. 6) the caking of the tablets stops in the Liquid on.

In a further experiment, 200 tablets of copolymer B are added to dispersion no. 1, without breaking them into lumps beforehand, the solution is decanted and the tablets are placed on polyethylene terephthalate film dried in the oven three times for 5 seconds each in rapid succession at i 70 ° C. The tablets begin to melt and become very sticky; after cooling, they are but essentially free flowing.

Example 3

200 g tablets of copolymer B are in 1000 ml of a 10% dispersion of Co-ο for 1 minute Polymer C was gently stirred. The tablets are drained and dried by passing a through them Airflow while on a sieve. The dried tablets (pearls) are after investigated the following test for their relative caking.

Caking test

1. 150 g of polymer beads are weighed to an accuracy of ± 1 g and placed in wide-necked, 236 cm ³

Bottles (16.5 χ 5.4 cm) introduced. These pearls form a layer about 8.9 cm high.

2. A cylindrical 1.4 kg weight is placed on the beads 5.1 cm in diameter and 8.9 cm in length, which is loosely inserted into a 0.025 mm thick poly-

Ethylene foil is wrapped so that the pearls are loaded ^{with approximately 0.07 kg / cm 2.} This corresponds to the pressure that prevails at a depth of 1.2 m in a bulk storage container or filling truck that contains these polymer beads.

3. The filled and loaded bottles are at the selected temperature for the selected Maintained for a period of time in a constant temperature air oven.

4. After the respective storage period in the oven, the filled and loaded bottles are removed from the

The oven was removed and left to cool to room temperature, still below the test weight. Then the weights are removed from the polyethylene sheet (which prevents the pearls from falling on the Weight sticking) is removed and the sample bottles are capped without theirs Getting content moving.

5. The tendency of the pearls to cake is then assessed by looking at the bottles and subjecting its content to a series of displacements of progressively increasing severity. With everyone Experimental severity is the extent of caking measured by the percentage of the entire polymer bead sample determined, the

is loose and can flow freely. This is done according to the following evaluation program:

a) The capped bottles are carefully placed on their side for 1 minute Leave it in place and evaluate;

b) the capped bottles are carefully turned upside down (with the Mouth down) and let stand upside down for 5 minutes. The time at which the Pearls fall off and the percentage of pearls that fall off is recorded.

It is also expedient to carry out each test with one or two comparative polymer samples so that the new product can be compared directly with the behavior of known substances.

An overnight test at room temperature gives the relative values listed in Table II Observations.

Table II

sample On the website Vice versa Copolymer B few pearls Lump fall down fall after several Minutes low Copolymensate B, a bit long all pearls coated with smarter Flie except the Copolymer C eat than at Soil layer Copolymers fall into sat D 20 seconds low

sample

Copolymer D

Copolymer A

On the website

almost free flowing,
Movement in 30 seconds Free flowing

Vice versa

all pearls

fall into

30 seconds

low

all pearls

fall immediately

low

It follows from these values that the improvement made possible by the coating of the copolymer B was achieved in the caking, the unwieldy behavior of the copolymer B into that of the almost free-flowing copolymer D can transform.

Example 4

According to the coating process of Example 3, two harder types of copolymers are coated and examined for caking improvement. The one used in this case Dispersion of the copolymer E has a solids content of 10%. One carried out within an hour Caking test gives the results summarized in Table III.

Table III

on the website 35 ° C vice versa on the website 45 ° C vice versa instant immediately slow after 5 min. Copolymer D Fall down Fall down 95% liked it instant immediately enough after 30 sec. Copolymer D, Fall down 95% liked it coated with Copolymer E enough Pearls fall slow after 2Vi ^Mm Copolymer F down in 2 seconds Fall down 95% liked it immediately immediately enough after 60 sec. Copolymer F, 95% liked it coated with Copolymer E immediately immediately enough after 20 sec. Copolymer G 95% liked it immediately immediately immediately immediately Copolymer A

From these data it can be seen that the caking of the copolymers D and F by coating with the copolymer E can be improved so much that these pearls are like pearls from the Copolymer G behave. Although this represents a technical advance, it is less noticeable is than the progress observed with copolymer B.

Example 5

After the coating process of Example 3, a sample of copolymer B beads with the Coated dispersion of the copolymer E described in Example 4 and in a long-term test Caking examined. After 8 months there will be a slight deterioration in the Caking improvement observed; but the sample is in terms of caking still far superior to the original material. The results are given in Table IV.

Table IV

1 hour at 24 ° C age on the website ITag slowly, many Pearls fall low 8 days slowly, many Pearls fall low 14 days slowly, many Pearls fall low 30 days very slowly, few pearls fall down vice versa, Time until Fall down from 100% (Sec.) 6th 13th 6th 12th

1 continuation at 24 C I hour age on the ropes 54 days very slowly, few pearls fall down 2V2 months very slowly, few pearls fall down 4 ^l / ₂ months very slowly, few pearls fall down 5 months very slowly, few pearls fall down 8 months very slowly, few pearls fall down 3; e i s ρ i e 1 6 vice versa. Time until Fall down from 100% (Sec.) 19th 18th 38 27 32

Larger quantities of tablets coated from the dispersion are produced in a V-blender. 22.7 kg of copolymer B are broken up and 19 1 of a dispersion of copolymer E with a Solids content of 10% added. The mixing time is 1 to 2 minutes. The dispersion is allowed to run off and determines the final solids content on a sample of the dispersion to reflect the weight gain to calculate the coated polymer. The mixer is then connected to an air line, whereupon air is passed through alternately for 25 minutes and the tablets for 5 minutes subjected to a tumbling motion until the tablets are dry. The product is free flowing and has a calculated coating of 0.3 weight percent.

Example 7

200 g of a caking copolymer of 59.5% ethylene, 37.3% isobutyl acrylate and 3.2% methacrylic acid (Shore hardness 57) are according to the method of Example 3 with a 10% dispersion of the copolymer E coated. The one with the copolymer of ethylene and vinyl acetate coated tablets have the caking behavior given in Table V, the achieved Improvement is most evident on the 24 hour test.

Table V

On the website Vice versa;
Time until
Fall down
from 100%
(Sec.) 1 hour at 25 ° C
Control 15 sec. Movement
coated 10 sec. movement 4th
1

5 1 hour at 30 ^° C Vice versa; 7th Control 20 sec. Movement Zeil until 6th On the ropes coated 10 sec. movement Fall down ¹⁰ 24 hours at 25 ° C from 100% 3V ₂ min. Control slowly (Sec.) 14th coats slowly

Example 8

30 g copolymer of 55% ethylene, 40% propylene and 5% hexadiene (Shore hardness 17) are in irregularly shaped blocks cut and immersed in a 10% dispersion of copolymer E. After drying overnight, the 3 hour caking test shows stronger cold flow, than is observed in copolymers of ethylene and vinyl acetate. They break when stirred coated particles and remain largely free. It is difficult for the original material to break out and quickly clumps together again into a solid mass.

Example 9

According to the procedure of Example 3, 200 k% sticky (soft) copolymer of 56% ethylene, 31% vinyl acetate and 13% carbon monoxide in the form of tablets by dipping into 10% dispersions of copolymer E are coated.

The results of a 1 hour caking test! at 24 ° C are summarized in the table below collected. Copolymer D is used as a comparison material

Table VI

Ethylene vinyl acetate
CO copolymer
coated

Ethylene vinyl acetate
CO copolymer
(Control)

Copolymer D

Time (% fall)
on the side | vice versa

20 sec. I 8 sec. (98%)
Move
(Flow of the individual tablets)

25 sec. 9 sec. (98%)

Move
(Flow as a soft agglomerate]

5 sec.
Move

1 sec. (100%)

The improvement is that the coated tablets separate from one another as they flow while the uncoated comparative polymer flows in the form of an agglomerate.

Claims (1)

Claim: Ethylencopolymerisattabietten of reduced stickiness, consisting of with a release agent coated polymer tablets, characterized in that the tablets consist essentially of an Äthylencopolymerisatkern with a macroscopic smooth, permanent coating in the form of a partial coalesced film made from a harder, less sticky type of ethylene copolymer is coated.