DE2256480A1 - Expandable alpha-olefin copolymer granules - having improved shelf life - Google Patents

Abstract

Olefin polymer granules, which are capable of being foamed by dielectric heating, comprise a) particles of a copolymer formed from 70-95 wt. % 2-6C alpha-olefin and 30-5 wt. % 3-8C alpha, beta-monoethylenically unsatd. carboxylic acid, and b) 2-25 wt.%, based on copolymer, of satd. perchlorofluorocarbon. Pref. the compsn., in which the copolymer is prepd. from ethylene and acrylic acid, contains excess NH3 and a thermosensitive nitrogenic releasing agent (e.g. p, p'-oxybisbenzenesulphonyl hydrazide) in order to improve foaming.

Description

EXPANDABLE COPOLYMERS It has been found that copolymers made from ° t-olefins and i (3 monoethylenically unsaturated acids an increased retention of organic Possess blowing agents and foam into foams with low densities, if they are plasticized by heating.

If you have such copolymers in series with an organic blowing agent and treated with NH3, they expand to 20 to 24 times their volume below Formation of permanent foams. They retain their foamability at room temperature for at least 27 hours. As was further found, pure ammonia can act as an expanding agent can be used for such copolymers. With these masses, a volume expansion can be achieved to more than 20 times after the impregnated particles or Have stored granules in the atmosphere for at least 4 hours.

This invention is also directed to new cellular thermoplastics and teaches the use of dielectric heat for foaming and fusing of copolymers an olefin and a bC) p -monoethylene unsaturated acids, causing foaming and melting quickly.

and is effective without the use of aqueous electrolyte mixtures will.

Electric heating is well suited for foaming processes, since it is a method in which the heat is rapidly and uniformly within a homogeneous material can be generated. However, the prerequisite is that the mass contains materials that have a high electrical loss factor and as a result, heat up rapidly in a high frequency electric field.

This invention is also directed to poly-d-olefinic materials, which can be foamed in the form of particles, the particles being a strong Volatile organic blowing agents have increased capacity under storage and foaming conditions to withhold. The invention also relates to polytolefinic copolymeric ones Masses that are in the form of particles and have a greatly increased retention capacity for an ammonical propellant, with the particles after storage foamed into cellular masses using dielectrically generated heat can be. The heating process for an expandable granulate can be important be when the loss of the propellant is great. In conducting the heat to the granules A temperature gradient emerges from the surface of a liquid or a gas to the inside of the granulate until a thermal equilibrium is established Has. The permeability increases with temperature and with the loss of crystallinity to. Here the granules can contain a considerable amount of propellant lose - before the core of the granulate particles is warm enough to foam up. When using high-frequency electrical heating, the interior of the particles is heated faster, so that the surface layers cannot be sufficiently plasticized, to flow under the influence of the internal inflation pressure. It has now been found that expandable particles of olefinic copolymers faster and to a larger size Volume in a high frequency electric field (27 MSIz) than in an air oven, In an oil bath or a steam atmosphere.

To explain this phenomenon it should be pointed out that pure Polyethylene containing 14.2% by weight dichlorotetrafluoroethane as a blowing agent, when Heating in oil to 1200C only foams to 4 to 5 times its volume. The use of dielectric heating is in the case of pure polyethylene and the pure polypropylene also unsatisfactory, since the loss factor of this Polymer is too low to obtain effective dielectric heating. If in contrast to this and according to the invention, various copolymers of ethylene with acrylic acid and propylene with acrylic acid with a liquid organic If propellant and / or ammonia are impregnated, a great improvement occurs the storage stability and the foamability compared to the pure homopolymers a.

The copolymers of unsaturated acids and olefins are random copolymers of the present invention and graft copolymers Consideration. These copolymers are commercially available and can be obtained by a Manufacture of a variety of well known methods.

It applies to the invention both in the case of random and graft copolymers it is preferred that the copolymer contain 70 to 95% by weight of bound olefin and 5 to 30% by weight contains bound acid.

For the production of the copolymers, monoolefins with 2 to 6 Carbon atoms per molecule are used, such as ethylene, propylene, l-butene, 1-pentene, 2-pentene, 1-hexene, 3-hexene, 3-methylbutene-1, 4-methylpentene-1 and 4-methylhexene-1. In general, for reasons of economy and also because of the good copolymerizability with acids ethylene and propylene the preferred olefins. A homopolymer of these Olefins can also serve as a substrate for the grafting of the unsaturated acid.

Any acid can be used as the d, 5-monoethylenically unsaturated carboxylic acid this type can be used with 3 to 8 carbon atoms in the molecule, dealing with allows copolymerization of an olefin of the type characterized or for grafting on homopolymers of olefin is suitable. Examples of such acids are monocarboxylic acids and polycarboxylic acids, such as acrylic acid, methacrylic acid, ethacrylic acid, crotonic acid, Isocrotonic acid, tiglic acid, angelic acid, senecioic acid, fumaric acid, maleic acid, Itaconic acid and citraconic acid. The preferred acid is acrylic acid. In In this context, it should be noted that the term "acid" in this Case also includes acid anhydrides, insofar as the monoethylenically unsaturated ones Acids form such anhydrides as e.g.

Maleic anhydride. The term "acid" includes such anhydrides, because they have the same reactivity as the free acids. The designation “Acid” also includes metallic or other salts of carboxylic acids and monoesters of polycarboxylic acids, e.g.

acid methyl maleate, acid methyl fumarate and acid ethyl fumarate.

The copolymers that are suitable for the invention are by no means limited to binary copolymers. For example, the copolymer can contain more than 1 olefin contain and / or more than one carboxylic acid. Ionic hydrocarbon copolymers can also be used can be used with good success in the present invention.

The invention is explained in more detail in the following examples.

Example 1 There are three 10 g samples of different granular polymers in glass ampoules with enough dichlorotetrafluoroethane added so that the particles are covered. The ampoules are sealed for 48 hours 75 ° C stored and then cooled to -73 ° C and opened.

The amount of dichlorotetrafluoroethane in the granules is initially and determined by weighing after storage in the open atmosphere.

In the following Table 1 are the compositions of the polymers and the measured values are given.

Table I polymer gram C2F4Cl2 per 100 g polymer according to the specified Storage time in an open atmosphere at 22 ° C beginning 2 20 44 116 pure polyethylene 13.2 10 6 3.8 2.1 92% ethylene - 8% acrylic acid 12.8 11.5 8.8 7.3 4.8 70.1% ethylene -29.9% acrylic acid 15.8 15.6 15.0 13.9 13.7 From these values are the relative time periods included for a 20% loss of the initial C2F4C1 are necessary as follows: pure polyethylene 1 92% ethylene - 8% acrylic acid 3.2 70.1% ethylene - 29.9% acrylic acid 56 After about 24 hours of storage on In the free atmosphere the prode made of pure polyethylene expanded to the 4- bis 5 times when heated to 120 ° C in a silicone oil. After 48 hours only occurred an expansion to 2 to 3 times the volume. In contrast, it expanded the sample from the copolymer of 70.1% ethylene and 29.9% acrylic acid on the 7- up to 9 times after storage in the open atmosphere for 168 hours.

The granules made from this copolymer expanded in an electrical manner High frequency oven (27 MHz) very good, whereas pure polyethylene in one Oven would not foam up.

Example 2 A sample of the copolymer of 70.1% ethylene and 29.9% Acrylic acid was successively a pressure treatment with C2F4C12 and NH3 in one subjected to sealed glass ampoule at 750C. The values for this treatment are given below: Weight of the starting polymer = 13 936 g with C2F4Cl2 impregnated polymer (24 h) at 75 ° C - 16 060 g (# 15.24 g / 100 g polymer) NH3 + C2F4Cl2 + polymer (3 h in NH3 at 75 ° C) = 17 303 g (# 8.91 g NH3 / 100 g polymer) Table II contains the data for the foaming behavior of these Polymers reported in a dielectric oven at 27 MHz.

Table II Stress behavior of a granulate made from a 70.1% ethylene - 29.9% acrylic acid copolymers impregnated one behind the other with C2F4Cl2 and NH3 (according to 27 h storage in an open atmosphere) Vf / Vs after aging of the foam Voltage gradient time to max. At 22 ° C for specified times (cm) (volts / cm) Volume (sec.) 0.2 h 3 h 30 h 2.54 1,000 1 - 2 collapsed-5.08 460 6 - 7 6 6 6 7.62 300 17 -18 24 21 20 10.16 230 39 20 19 18 These values show that the combination of dichlorotetrafluoroethane and NH3 leads to expandable particles, which under atmospheric conditions at least.

Can be stored for 24 hours without significant loss to suffer from foamability. The Nile treatment has some desirable effects for the 3 foaming behavior of ethylene-acrylic acid copolymers impregnated with dichlorotetrafluoroethane: 1. faster heating in the area of radio frequencies; 2. Nucleation for the cells (the cell size is reduced by a factor of 10 to 100) and 3rd expansion to lower density foams.

Example 3 A copolymer of 78.0% ethylene, 11.0% acrylic acid and 11.0% isobutyl acrylate is successively treated with pressure with ammonia and dichlorotetrafluoroethane subject. This copolymer absorbs 23 g of dichlorotetrafluoroethane per 100 g and 8 g of NH3 per 100 g. Part of the freshly impregnated granulate is poured into a dielectric oven with an electrode spacing of 10 cm. In the course of The granulate expands to 70 to 80 times its volume in 10 seconds. To however, storage for about 1 hour at room temperature shrinks the foam to about 8 to 10 times the volume of the granulate. The rest of the impregnated granules is stored at room temperature in the open atmosphere. After storage over Night becomes part of this granulate in a '' dielectric oven foamed, with an increase in volume of about 20 to 25 times. The foam does not collapse after cooling to room temperature. The rest of the Granules are stored in the open atmosphere for 2 days. After this storage will the granulate is foamed in a dielectric oven to about ten times its volume. These foam samples are all of high quality and have uniform, small cells.

Example 4 There are 12 g samples of pure polyethylene and ethylene Acrylic acid copolymers in granulate form sealed with liquid Nfl3 in 40 ccm Glass ampoules covered. The ampoules are stored at 220 ° C. for 64 hours. The granules are weighed immediately after removal from the ampoules, in aluminum weighing pans stored and reweighed after various periods of time. Simultaneously with the Observation of the loss of NH3 are samples of the granules in a dielectric Oven heated to investigate the foaming behavior. The values in the following Table show that ethylene-acrylic acid copolymers and NH3 as a blowing agent Can produce foams that are resistant to collapse in the atmosphere are. In contrast, NH3 does not penetrate sufficiently into pure polyethylene, to allow expansion to a low density foam.

Table III Dielectric foaming of ethylene-acrylic acid copolymers impregnated with NH3 After storage for various periods of time in the open atmosphere at 22 ° C Electrode distance 2.54 voltage gradient volts / cm = 1000 (1) 92% ethylene-8% acrylic acid copolymers Storage time, h 0.1 1.0 2.0 4.0 22.5 30.5 55.0 Total NH3 (g / 100 g P) 5.83 4.25 3.73 3.33 2.22 1.64 1.64 "free" * NH3 (g / 100 g P) 3.94 2.36 1.84 1.44 0.33 0 0 Foaming time, sec. 4.4 3.7 7.4 8.3 17.2 15.2 22.3 foam volume, initially ** 22 21 18 20 1.5 1.5 1.5 foam volume after 48 h at 22 ° C 15 14 12 12 Tabel III (continued) (2) 70.1% ethylene-29.9% acrylic acid copolymer storage gradient, h 0.1 1.0 2.0 4.0 22.5 30.5 55.0 Total NH3 (g / 100 g P) 17.27 14.63 13.57 12.67 10.08 9.63 9.15 "free" * NH3 (g / 100 g P) 10.21 7.57 6.51 5.61 3.02 2.57 2.09 expansion time, sec. 0.9 1.2 1.4 1.4 1.7 1.8 1.9 foam volume, up ** 29 22 19 24 2.3 1.6 1.4 foam volume after 48 h at 22 ° C 27.5 22 21 23 2.3 1.6 1.4 * "free" NH3 = total NH3 minus the NH3 theoretically required for salt formation ** Foam volume = ratio of the volume of the expanded particles / initial volume of solid particles Example 5 5 g of a copolymer were obtained from 70.1% ethylene and 29.9% acrylic acid successively with a pressure treatment Subjected to NH3 and C2F4C-12 in closed glass ampoules at 75 0C. After a Storage in the open atmosphere for 27 hours became the expandable granules placed in a 50 ccm bottle made of polypropylene and placed between the electrodes a 27 Mint dielectric furnace given. The electrode gap is 10 cm and after after exposure for 60 seconds, the vial is removed and its contents checked.

One notices that the particles expand and one with the other are sintered or fused. The foam obtained is tough and elastic.

Example 6 10 g of pp'Oxybisbenzenesulfonylhydrazid are with 90 g of one Copolymers of 92% ethylene and 8% acrylic acid mixed at 125 ° C. From this mixture a shaped body with the dimensions 5 x 5 x 0.25 cm is produced.

This shaped body is placed in a closed vessel with NH3 for 3 hours given at 75 ° C. After removal from the NH3, it was found that the sample experienced a 5.8% weight gain. After 2 hours at 220C the NH3 fell Focus on 3.5.

The aged sample (2 hours) expanded to 3 times its own Output volume in a 27 z dielectric oven in comparison 19 volumes with NAH 3 alone as a propellant, which means that the pp'Oxybisbenzenesulfonylhydrazid has decomposed with the formation of N2 and thereby to Expansion of the foam has contributed.

The dimensions of the foam sample in the final state were 14 x 14 x 0.7 cm.

Example 7 A solid copolymer of 88% propylene and 12% acrylic acid (Melt index 1.2) in the form of granules with grains with a diameter of 0.3 cm enlarged in a closed ampoule containing dichlorotetrafluoroethane, their weight by 11.8% in the course of 4 hours at 100 ° C. (Sample 7-1).

The granules containing the dichlorotetrafluoroethane was in a sealed glass ampoule treated with liquid ammonia for 3 hours at 25 ° C. The sample increased its weight by 4.85. (Sample 7-2).

Sample 7-1 was heated in a 27 MHz dielectric oven for the plasticization and foaming is insufficient.

Sample 7-2 foamed in such an oven with an electrode gap 2.54 cm to a cellular product with the volume increased 6.2 times.

For the dielectric foaming, a Thermex 7 RB became more dielectric Furnace used with a power of 7.5 KV at 27.32 mhz. The manufacturer of this Ofens estimates that the RF voltage for 38 x 38 cm electrodes is 20KV when the distance of the plates is 5.7 cm.

This oven is capable of producing a maximum of 107.5 kilocalories each Minute to deliver a material that would absorb all of its energy. The proportion of this potential energy that is converted into usable heat, depends on the dissipation factor of the dielectric and its amount in the field between the electrodes.

Volatile organic compounds can be used as blowing agents in the invention can be used alone or together with NH3, as well as heat-sensitive nitrogen-releasing agents Connections in connection with NH3.

Examples of suitable volatile organic compounds that May be used in the invention are preferably aliphatic or cyclic Perchlorofluorocarbon compounds. Examples of suitable compounds of these Type are: CC13F CF3 - CC1F2 12 2 CF2 - CC1F CC1F3 CF2 - CF2 CCl2F - CCl2F CF2 - CC1F CC1F2 - CCl2F CF2 - CC1F CC1F2 - CC1F2 Mixtures of two or several such volatile organic compounds can be used.

Heat-sensitive nitrogen-releasing compounds are, for example, benzene sulfonyl hydrazide, pp'-oxybisbenzenesulfonyl hydrazide and N, N'-dinitroso-N, N'-dimethylterphthalamide.

However, the propellants are not limited to those mentioned here and in the Examples of compounds used are limited.

Rather, other substances known as propellants can also be used or are suitable.

When choosing a propellant, care is generally taken stated that the propellant had a low permeability value for the passage through the polymer has. The permeability (P) is a function of the diffusion coefficient (D) and the solubility, so that the formula applies P = DS.

The usual method for achieving a low permeation rate consists in choosing a propellant with a large molecular diameter, this also has a significantly different solubility parameter (S) as the polymer. This applies, for example, to those mentioned above Perchlorofluorocarbon blowing agent too. However, the solubility (S) must not be be low, otherwise the maximum concentration of the propellant in the impregnated Granules for expansion into a cellular, low density product do not is sufficient. With regard to the heat-sensitive nitrogen-releasing compounds it should be noted that the solubility of N2 is quite low and the N2 molecule is relatively small. Nevertheless, when using these connections in combination excellent results with NH get like this from example 6 can be found.

This is probably due to the fact that the thermosensitive Material is insoluble in the polymer or copolymer and is in the form of discrete particles. When the N2 gas is released, this leads to excellent nucleation for foaming. By modifying the Olefin polymers by interpolymerization with polar monomers such as acrylic acid, the solubility parameter is likely to be increased.

There is no intention to relegate the invention to any particular arrangement or mode of operation or conditions to restrict as these factors are within broader range Limits depending on the particular copolymer used, the treatment time vary with the electrical energy, the frequency used and the like can. However, these variables do not present any difficulties for the person skilled in the art to be coordinated for the specific individual case.

The frequency of the electric field can also be within wide limits fluctuate and generally get good results with a frequency of 6mhz up to 200 MHz. Difficulty finding an optimal general frequency as these have different electrical and chemical characteristics depend on the compounds in question. The optimal frequency can, however can be determined very easily by taking some values in the above range being checked.

A particular advantage of the method according to the invention is that that by using high frequency heating at very high working speeds compared to the usual foaming can work, creating a considerable Saving in time, manpower and equipment is possible.

In the invention, expandable compositions of copolymers of 4-olefins and C,, ß 5-monoethylenically unsaturated acids produced when Warming them will soften and lightly dry in a high frequency electric field lather up. This is particularly advantageous for dielectric foaming of expandable films, sandwich structures. The method is also suitable of the invention is also particularly good for the manufacture of packaging materials.

Claims (10)

Claims 1. Expandable olefin copolymer composition comprising 70 to 95% by weight of a Olefins having 2 to 6 carbon atoms and 30 to 5% by weight of an i, ß -monoäthylenisch contains unsaturated carboxylic acid with 3 to 8 carbon atoms in the molecule, thereby characterized in that the copolymers contain an organic blowing agent or ammonia and the compositions are foamable by dielectric heating and have a shelf life of at least 4 hours when stored in the open atmosphere and at room temperature to have. 2. masses according to claim 1, characterized in that they are 2 to 25 % By weight of a saturated perchlorofluorocarbon, based on the weight of the copolymer, contains. 3..Mass according to claim 2, characterized in that it contains ammonia in excess of that required for the neutralization of the carboxyl groups Amount contains. 4. Mass according to one of claims 2 or 3, characterized in that that the saturated perchlorofluorocarbon is 1,2-dichlorotetrafluoroethane. 5. mass according to claim 1; characterized in that they contain ammonia in excess of that required for neutralizing the carboxyl groups Amount contains. 6. Composition according to one of claims 1 to 5, characterized in that that the copolymer is a copolymer of ethylene and acrylic acid. 7. Process for the production of cellular thermoplastic masses a copolymer of 70 to 95% by weight of an i-olefin having 2 to 6 carbon atoms in the molecule and from 5 to 30% by weight of a (3-mono-ethylenically unsaturated carboxylic acid with 3 to 8 carbon atoms in the molecule, characterized in that an organic Propellant or ammonia in excess amounts compared to that for the combination with the carboxyl groups required amounts, are incorporated into the masses and the masses obtained by the action of a high-frequency electric field can be heated at 6 to 200 megacycles per second. 8. The method according to claim 7, characterized in that the di0lefin Ethylene or propylene, the carboxylic acid is acrylic acid and the organic blowing agent 1,2-dichlorotetrafluoroethane is. 9. The method according to claim 7, characterized in that the Copolymers with 2 to about 15% by weight of a heat-sensitive nitrogen releasing agent By means of and with ammonia in excess amounts, compared to those for the combination with the carboxyl groups required amounts, mixes and then the mixture obtained heated in a high frequency electric field. 10. The method according to claim 9, characterized in that the olefin Ethylene, the @carboxylic acid acrylic acid and the heat-sensitive nitrogen splitting off Compound is pp'oxybisbenzenesulfonylhydrazide.