DE1104681B - Method for joining irradiated polyethylene parts - Google Patents

Description

Method of joining irradiated polyethylene parts The invention refers to the joining of parts made of polyethylene, that of a high-energy one Radiation, such as gamma rays, high energy electrons, has been exposed. Here connections result which have good strength at room temperature and optionally remain solid even at an elevated temperature above 1000 C.

It is known to irradiate polyethylene with high energy Radiation, especially with high-energy electrons, to make it soluble in various solvents, such as toluene, xylene, to reduce and to crosslink it, so that it is no longer thermoplastic but is practically insoluble. This Polyethylene has a reduced flowability at elevated temperatures, which is below certain irradiation conditions at a temperature of about 150 to 2500 C and can even be completely absent from it. These properties are e.g. B. responsible for that the polyethylene is resistant to steam sterilization without deformation. Irradiated Polyethylene is also resistant to breaking in the presence of certain organic substances Resistant to stress.

However, when using irradiated polyethylene for various purposes, e.g. for sterilizable containers, e.g. for food or medicines, the filling either before or after exposure to high-energy rays is made, it is often desirable to hermetically seal the container, to make its contents sterile at an elevated temperature in the autoclave. The one to connect Common methods of ordinary polyethylene have proven to be used for joining parts Made of irradiated polyethylene not proven, If you try the surfaces of irradiated polyethylene, which with higher radiation doses in the order of magnitude from about 6 to 10 to 106 R has been irradiated, then combine in the heat shows that under practically applicable conditions, for example at about 2300 C and an exposure time of about 0.5 seconds, the bond at room temperature is pretty weak. A connection obtained in this way is generally already at a temperature of about 1250 C no longer adhesive strength and dissolves at this Temperature slightly under load.

In some cases you can get a pretty good one at room temperature Achieve connection by removing the surfaces of irradiated polyethylene bring them into direct contact with each other under heat. However, the prerequisite is that the polyethylene has a low radiation dose, usually from about 1 to 3 106R. However, it has also been found here that at an elevated temperature of about 1250 C the connection is extremely weak and below breaks easily.

Surprisingly, it has now been found that you have a connection of parts made of irradiated polyethylene according to the invention can achieve that a free radical generating hardener on at least one of the to be bonded Applies parts and in a known manner using heat and pressure united with each other. You not only get between surfaces of irradiated Polyethylene that has been irradiated with low doses of radiation, but even between surfaces of irradiated polyethylene that is exposed to higher radiation doses, for example, with doses up to 10 to 50,106 R, has been irradiated, strong bonds. The connection is not only strong at room temperature, it also holds one withstand heavy loads at elevated temperatures of around 1250 C and above for a long time. The hardeners are those usually used to harden non-irradiated polyethylene can be used.

In Fig. 1 the end sections 1 are flat irradiated polyethylene parts shown, one of the inner surfaces having a thin coating of a curing agent for thermoplastic polymers.

Fig. 2 shows a cross-section of the connection that can be seen after Fig. 1 receives.

Fig. 3 illustrates a further embodiment of the invention, wherein the surfaces of a part 1 made of irradiated polyethylene with a thermoplastic Polymer 3, for example, made of non-irradiated polyethylene, brought into contact which has been previously coated with a thin film of a hardening agent 2 is.

FIG. 4 shows the connection obtained according to FIG. 3.

FIGS. 5 and 6 explain a further embodiment of the invention, wherein the hardening agent 2 is applied to both contact surfaces of the parts before the connection 1 made of irradiated polyethylene is applied.

Instead of the intermediate layer made of a thermoplastic polymer, As shown in Fig. 4, the hardener can also be intimately divided into a finely divided thermoplastic polymer, e.g. B. with polyethylene, mix and the mixture on Apply the surfaces to be connected to the irradiated polyethylene.

The implementation of the method according to the invention depends on various factors Factors, e.g. B. whether the polyethylene with higher or lower radiation doses has been irradiated. A polyethylene that has a dose of about 2 to 20,106 R has been irradiated, gives strong at room temperature (about 25 to 35 ° C) Ties. The way in which the connection between the brings parts to be connected can be varied widely. A possibility consists in applying a coating of the compound that generates the free radicals, hereinafter referred to as curing agent, either on or on both contact surfaces of the irradiated polyethylene, e.g. B. in the form of a solution or dispersion. In this case or even if you have the hardener Applied in dry form, it needs the amount of on the surfaces of the irradiated Polyethylene applied curing agent not to be very large.

When using solutions such. B. in xylene, toluene or benzene is sufficient a concentration of about 2 to 15 percent by weight based on total weight the solution. The use of higher or lower concentrations is not excluded.

After evaporation or evaporation of the solvent, the irradiated polyethylene surfaces under the action of heat and pressure in direct Brought into contact with each other. If you put the curing agent on polyethylene that irradiated at a low dose is strength the bond both at room temperature and at elevated temperature, i.e. at about 125 to 1500 C, very good. However, if the same procedure is used with polyethylene, that has been irradiated with higher doses, for example about 25 up to 50,106 R and above, then it turns out that you can get a good bond strength though at normal temperature, however, in terms of the strength of the Room temperature for bond obtained with low dose irradiated polyethylene does not correspond. At a higher temperature, the bond strength is Polyethylene irradiated with a higher dose and too weak for many types of use.

NIan can increase the durability if you choose between the Surfaces of the irradiated polyethylene are organic, thermoplastic, polymeric Substance that is hardened by the hardener brings and uses it as an adhesive substance used. The surfaces of the irradiated polyethylene are then brought into direct contact Contact with the thermoplastic polymer and curing agent mixture described above and joins the assembly by applying heat and pressure. In this way one obtains bonds that are not only good at room temperature, but also at elevated temperatures Temperature are good even with high tensile load. When you think of the thermoplastic Polymer with the hardening medium used, it should be noted that the hardened thermoplastic Polymer that is placed in the bonding area through the application of heat and pressure when Sealing, at the high temperatures, should have properties that are compatible with the properties of the irradiated polyethylene are comparable, so that the uniform Structure obtained from the adhesive and the irradiated polyethylene, a has substantially uniform heat resistance.

This type of connection can also be used for irradiation at lower doses Use polyethylene.

Examples of suitable thermoplastic polymers are solid, not irradiated polyethylene, polypropylene, copolymers of ethylene and vinyl acetate, Copolymers of butylene and other olefins, for example copolymers of isobutylene and ethylene, isobutylene and isoprene, etc. Generally preferred polyethylene having a molecular weight of 12,000 to 35,000 is determined by the intrinsic viscosity, because you get a particularly uniform connection.

Also for joining surfaces of irradiated polyethylene by means of a mixture of the thermoplastic polymer and the curing agent consider several options. So you can get a crushed solid thermoplastic Polymer, for example polyethylene, with the curing agent, for example with Benzoyl peroxide, mix and apply the mixture to the surfaces to be joined.

One can also use a thin sheet or film of the thermoplastic Polymers, e.g. B. having a thickness of about 0.0254 to 2.54mm or more on both Cover the sides with the hardener and place the coated film between the Lay the surfaces of the irradiated polyethylene that are to adhere to one another.

The thermoplastic polymer can e.g. B. with a 1 to 15 percent by weight dilute aqueous or organic solution of the hardener are treated. Instead of applying a coating to the surface of the thermoplastic polymer, for example, it can be immersed in a solution of the hardener, the solvent evaporate or, through application of heat, which is insufficient, the free radicals decompose the generating compound, remove it and then make the connection. Finally, the curing agent can also be applied to the surfaces of the irradiated Apply polyethylene and the thermoplastic polymer with or without additional Put a coating of hardening agent in between and perform the heat seal.

The connection of the polyethylene parts is always done with the usual Heat sealing devices in a heat and pressure treatment to create a flow and curing the unirradiated polymer and strongly bonding the surfaces to achieve the irradiated polyethylene.

The irradiated and the non-irradiated polyethylene, which is used in the The present process used is a polymeric, through polymerization polymeric polymer produced from ethylene usually at high temperature and high pressure Material. It has N molecular weights, for example, from 15,000 to 30,000 and above, determined by the intrinsic viscosity. Preferably that is Molecular weight in the range from 19,000 to 25,000.

The irradiated polyethylene can have various flat shapes Raw materials, usually of uniform thickness, for example in the form of flat sheets.

Ribbons, films, flattened or U-shaped Hoses exist in which the film or tape sheet is half bent so that a U-shaped body results in which the legs of the U are parallel, etc. Also Fillers, such as silicon oxide or carbon black, can be used in amounts from 0.5 to 35 percent by weight or above based on the weight of the polyethylene in which not irradiated or irradiated polyethylene.

All inorganic or organic peroxide compounds can be used as hardeners which are able to form free radicals. Examples are barium peroxide, Sodium peroxide, aliphatic acyl peroxides such as acetyl peroxide, lauryl peroxide, stearyl peroxide, peroxides of the aromatic acid series such as benzene peroxide, mixed organic Peroxides, such as acetylbenzoyl peroxide, ketoperoxides, such as acetyl peroxide, triacetyl peroxide, Hydrogen peroxide and alkyl derivatives of hydrogen peroxide, such as monoethyl peroxide, Diethyl peroxide, di-a-cumyl peroxide, t-butyl-a-cumyl peroxide, the two last named peroxides are preferred for curing polyethylene, peresters, such as perbenzenic acid t-butyl ester, diperphthalic acid di-t-butyl ester, hydroperoxides, such as t-butyl hydroperoxide, various per compounds such as perborates, persulfates, Perchlorates, aliphatic azo compounds such as 2-azobisisobutyronitrile, organometallic Compounds such as tetraethyl lead, tin tetraphenyl, benzoyl peroxide. Di-t-butyl diperphthalate and dicumyl peroxide are preferably used as the hardening agent.

The amount of curing agent can vary within wide limits, and depending on the temperature and pressure used during the sealing process Type of irradiated or non-irradiated polyethylene used, the irradiation dose, to which the irradiated polyethylene has been subjected.

In general, when using intimate mixtures of the in Particles averaging 5 to 200 microns in diameter are present thermoplastic, non-irradiated polymer and curing agent desirable, that you have about 1 to 159 / o curing agent or more, based on the weight of the not irradiated polymer is used.

In general, both the pressure and the temperature can be used the length of stay, d. H. the time within which pressure and temperature are maintained will vary widely, depending on factors such as the type of used irradiated polyethylene, the radiation dose introduced into the polyethylene, the Type of thermoplastic polymer used, the curing agent used etc. As will be immediately apparent to those skilled in the art, there is a dependency between Temperature, pressure and dwell time. In general, pressures in the range of 0.07 to 3.50 kg / cm2 or more on the contacting surfaces of the irradiated Apply polyethylene. Temperatures of about 149 to 2600 C are moderate, it should be noted that the higher the temperature, the shorter the residence time or the time during which the compound is exposed to pressure and elevated temperature is exposed. So it is advantageous, depending on the temperature and pressure, at 149 to 2600 C times of 0.2 to 15 seconds and more must be observed.

In the following examples, all parts are parts by weight.

About the strength of the seals obtained in the following examples to check, the procedure was as follows. All heat seals were made with a "Model 12 A sentinel, heat sealer" from Packaging Industries Co. with a Teflon-coated Press jaws of the size 2.54X30.48 cm are made. An automatic control device allowed a pressure of up to 6.3 kg / cm2 on the press jaws to be carried out Temperature up to about 2600 C and a dwell time of 0.25 to 15 seconds. All Samples were measured for expansion to break in a Scott tensile tester. The polyethylene tested was a film about 0.0381 cm thick. A Tape with the standard width of 2.54 cm was used for testing both at room temperature (250 C) as well as used at elevated temperature and the result as to breakage required grams specified. Tape samples with a width of 2.54 cm were examined, while film samples in film form became velr hours, resulting in one inch wide Strip cut. The polyethylene used had a molecular weight of about 21,000. The connection took place at a pressure of 2.10 kg / cm2 and in the examples specified temperatures and residence times. The durability at high temperature was determined to be the time that a 2.54 cm wide bonded strip would apply a load of 15 g at a temperature of 1250 C. Unless otherwise stated, was the peroxide used as 100 / above solution.

Example 1 The ends of a strip of unirradiated poloethylene were sealed together under the conditions given in the following table.

In addition, other samples of polyethylene were used, which with a dose of 5 or 10 106 R had been irradiated. Also the method of manufacture the connection was varied. In one case, an interlayer did not become one irradiated polyethylene film about 0.038 mm thick and wide of about 1.27 cm placed between the layers of irradiated polyethylene, and although partly without further treatment, partly after a treatment in which the intermediate layer about 3 hours in a 10% solution of the peroxide given in the table was immersed in benzene. The treated intermediate layer was then allowed to dry, so that a coating of hardener remained between the surfaces of the irradiated polyethylene to be sealed came to rest. In certain cases the curing agent was applied directly to the irradiated polyethylene.

Another modification consisted in using solutions of finely divided, non-irradiated polyethylene and the organic peroxide in question in hot Xylene produced and this solution on the surfaces of the irradiated polyethylene spread.

Finally, a further modification was finely divided, not Providing irradiated polyethylene with a coating of an organic peroxide by the two substances were suspended in benzene and the solvent evaporated. That Product was used as an adhesive on the two surfaces to be connected to the irradiated Brushed on polyethylene. Here were the percentages by weight of that which had not been irradiated Polyethylene and organic peroxide alike. The peroxides used were Benzoyl peroxide (B P) and di-t-butyl diperphthalate (D T B D P).

Table I. Type of procedure, strength, durability Irradiation needle to which the connection temperature dwell time at room connection dose | was made whether G in seconds temperature at 125 ° C in g / 2.54 cm Direct touch only 232 0.5 1910 5 seconds 1. Direct touch only 232 0.5 1184 30 seconds 2nd intermediate layer made of not 3 radiated polyethylene 232 0.5 1880 6 minutes Surfaces of irradiated No # polyethylene, with 10% iger 5.106 106 R xylene DTBDP solution coated 232 0.5 1740 4.5 hours (average) 4. Same as 3 199 0.5 1665 13 minutes (average) 1. Direct contact only 149 10 371 not measured 2. As 1 199 10 537 not measured 3. As 1 232 0.5 398 not measured 4. Same as 1 232 10 481 15 seconds 5. Surfaces of irradiated Polyethylene, with 10% benzene BP solution streak 149 0.5 348 not measured 6. As 5 149 10 576 not measured 7. As 5 199 10 647 not measured 8. Same as 5 232 10 636 25 seconds 9. As 5 232 0.5 526 not measured 10. Like 5, but usage from DTBDP instead of BP 232 10 595 25 seconds 11. Interlayer made of not None # Blasted Polyethylene 232 10 1610 10 minutes 10. 106 R 12. Intermediate layer made of not radiated polyethylene, with 100% benzene BP Solution coated 232 0.5 1470 8 hours *) 13. As 12 232 10 1530 6.25 hours *) 14. As 12, but usage from DTBDP instead of BP 232 0.5 1410 5.5 hours *) 15. As 14 232 10 1435 8 hours *) 16. Sylol solution with a content of 2 percent by weight not irradiated polyethylene and 2 ° / o DTBDP 232 0.5 1260 6 hours *) 17. Powdered, non-irradiated Polyethylene, with DTBDP coated (same weight parts) 232 10 614 5.75 hours *) :) The connection of the trial bush was not disconnected when the experiment was terminated.

In those cases where the strength is below room temperature Was 276 g / cm, the high temperature joint strength did not become certainly. It is interesting to note that at Experiment 3, where Polväthvlen used that with a dose of about 5. 106 R was irradiated, not a non-irradiated one Polyethylene was required, probably because the polyethylene was an adequate one Contained proportion of uncrosslinked polymer.

Example 2 The connection was made in each case at a pressure of 2.10 kg / cm2. Di-t-butyl diphthalic acid ester (DTBDP) was used as the peroxide. It got alone or with non-irradiated polyethylene in the form of a hot xylene solution with the help applied to a 1.27 cm wide, lambskin-covered roll.

The solution was allowed to dry before bonding.

The strength of the connection at room temperature became as in Example 1 by stretching a 2.54 cm wide strip on a Scott tester measured to break. An average of five to six determinations were made up made to break. The strength of the connection at high temperature was increased measured by placing a 2.54 cm wide strip at 1250 C under a load of 15, 30, 45 or 60g and measured the time to break. The results were then classified in the following ways: A. Endured exposure longer than Stood for 30 minutes.

B. Withstood 4 to 30 minutes of exposure.

C. Withstood exercise for less than 4 minutes.

Many of the compounds that work at 250 C under load for 30 minutes survived, were left in the furnace in which they were tested for a long time, and were still okay after 6 to 8 hours. Most of the connections that come with 1250 C failed, showed this in less than 4 minutes.

The loads used for these examinations indicated if when applied to a section of 0.0038X25.4 mm, the following tensile loads: Table II 15 g ................. 1.54 kK / Cm2 30 g 3.08 kg / cm2 45 g ............. ....... 4.62 kg / cm2 60 g .................... 6.16 kg / cm2 Those treated in Table III Experiments concern a polyethylene film with a dose of 5. 106 R irradiated and treated at the connection points with a solution containing only the peroxide had been. The results described in Table IV refer to a polyethylene film, which is irradiated with 10 106 R and with a solution containing 2 percent by weight of peroxide and contained unirradiated polyethylene. Those described in Table V. Results refer to film irradiated at a dose of 10 106 R. and then at the joints with a solution that is 5 percent by weight Peroxide and non-irradiated polyethylene, had been treated.

Table III Irradiation dose of film: 5 106 R Solution treatment: 5% peroxide in xylene Load dwell time in application in from heat g / 2.54 cm 0.5 seconds 1 second 2 seconds X 1550 1440 1550 Y 15 ABC AAB AAA 30 BBC ACC AAC 45 CCC CCC CCC 60 CCC CCC CCC X = g / 2.54 cm to break at room temperature.

Y = ability, at 1250 C, the load indicated in the next column (g / 2.54 cm) to wear.

Table IV Irradiation dose of the film: 10 106 R solution treatment: 2% peroxide + 2% non-irradiated polyethylene in xylene Tempe dwell time temperature 0.5 seconds 2.5 seconds 5 seconds OG XYXYXIY 1085 CCC 1165 CCC - - 149 # 962 CCC 853 CCC - - 876 CCC 1085 CAA - - 177 l 1105 CCC 1265 CCC - - 1250 1250 CCC 1385 CAA 1375 AAA 199 1300 CCC 1265 CCC 1250 AAA 1110 CCC 1170 AAA 1200 AAA 216 1055 CCA 1210 AAA 1325 AAA 1260 AAA 1160 AAA - - 232 l 1235 AAA 1325 AAA - - X = g / 2.54 cm to break at room temperature.

Y = ability to withstand a load of 5.91 g / 2.54 cm at 1250 C.

Table V Irradiation dose of the film: 10 106 R solution treatment: 5 ovo peroxide + 510 / o non-irradiated polyethylene in xylene Tempe load Dwell time during application from heat rature in OC g / 2.54 cm 0.5 seconds second customer x X 1330 149 Y 15 CCC 30 CCC X 1440 Y 15 AAA - - 199 q 30 AAA AAA AAA 45 AAA AAB ABC 60 BCC CCC CCC X 1160 y 15 AAA 232 30 AAC 45 CCC 60 CCC X = g / 2.54 cm to break at room temperature.

Y = ability, at 1250 C, that indicated in the next column To bear weight.

Example 3 Polyethylene tape of 0.0038 X 19.0 mm was, as described above, with different doses of high energy electrons ranging from 5 to 20. 106 R irradiated. Thereafter, the surface to be joined was the irradiated polyethylene coated with a 10 weight percent solution of dicumyl peroxide in xylene, the Cover dried in the air until all the xylene had evaporated, and then afterwards the film so combined in the heat by standing at 221 to 2260 C for 5 seconds exerted a pressure of 10.6 kg / cm2. Each of the connected specimens was checked putting it in an oven at 1250 C and placing it in the previous one both examples described loaded with 15g. As a result of these attempts it was found that the compounds of with doses of 5, 7, 5, 10, 12, 15 and 20th 106 R still irradiated polyethylene samples after 15 minutes intact was. This example illustrates the advantage that z. B. Dicumyl peroxide opposite other peroxides at higher radiation doses, but otherwise similar conditions offers. No unirradiated polymer was used.

The method according to the invention can advantageously be applied of insulating layers that are wrapped in a spiral around the conductor.

Also for closing sterilizable containers made of irradiated polyethylene film it works very well.

An application for which the present method is particularly the production of thick-walled containers from irradiated polyethylene film is suitable, which are usually composed of several parts. You can do any part irradiate for themselves and then connect them together.

The X-ray units (R) are defined as the amount of radiation which is an electrostatic charge unit in 1 cm3 of dry air under standard conditions produce. They relate here to the amount of electron radiation that is generated with a air-equivalent ionization chamber on the surface of the irradiated polyethylene was measured.

Claims (7)

PATENT CLAIMS: 1. Process for joining irradiated polyethylene parts, characterized in that a free radical-generating hardener is used at least one of the parts to be connected applies and in a manner known per se combined with the application of heat and pressure. 2. The method according to claim 1, in particular for use on polyethylene, which was irradiated with 25 to 50 106 R, marked by this net that one between the parts of the irradiated polyethylene to be connected a thin layer of a unirradiated thermoplastic polymer such as polypropylene or unirradiated polyethylene and a curing agent for thermoplastic polymers brings on top of which the parts combined in a manner known per se using heat and pressure. 3. The method according to claim 1 or 2, characterized in that as free radical curing agents for thermoplastic polymers, such as benzoyl peroxide, Cumyl peroxide, dicumyl peroxide or diperphthalic acid di-t-butyl ester, if appropriate s dissolved in an organic solvent, used. 4. The method according to claim 1 to 3, characterized in that one bonding at a temperature in the range of about 150 to 2600 C and at one Applies pressure of more than 0.45 kg / cm2. 5. The method according to claim 2 to 4, characterized in that one coats the unirradiated polymer with a layer of the curing agent. 6. The method according to claim 2 to 5, characterized in that one the unirradiated polymer in finely divided form, in a particle size of 5 to 2001lJ in particular, in an amount of 1 to 15 percent by weight, based on the unirradiated polymer, mixed with the curing agent and the mixture to at least applies one of the parts to be connected. 7. The method according to claim 2 to 6, characterized in that one the thermoplastic polymer used dissolved in an organic solvent.