KR900001559B1 - Expandable polyolefin composition and preparation process utilizing isobutane blowing agent - Google Patents

Abstract

A prepn. of a substantially closed cell olefin polymer foam having dimensional stability comprises (a) heat plastifying an olefin polymer resin (I) selected from homo and copolymers of ethylene, and a copolymerizable monomer (II), (b) mixing the resin from (a) with a stability control agent, and with a blowing agent, and (c) activating blowing agent to expand the mixt. to a closed cell polymer foam.

Description

Expandable Polyolefin Compositions and Methods for Making the Same

The present invention relates to an expandable olefin polymer composition and a process for producing the same, more particularly a modified expandable olefin polymer composition having dimensional stability using low cost isobutane as the primary blowing agent.

Thermoplasticize the normally solid olefin polymer resin and mix the thermoplastic resin with a volatile blowing agent under heating and pressure to produce a flowable gel, then extrude the gel to low pressure and low temperature to activate the blowing agent and expand and cool the gel Processes for producing olefin polymer foams are well known, by forming a desired solid olefin foam product.

A frequently encountered problem is the problem of preventing partially cured foams from shrinking to an unacceptable degree during emulation or curing after manufacture. During the soaking or curing period, the foam used gradually diffuses out of the bubbles in the foam product and air gradually diffuses into the bubbles instead of the blowing agent. Until very recently, only one volatile hydrocarbon blowing agent, i.e. 1,2-dichlorotetrafluoroethane, provided sufficient dimensional stability during the curing period to provide low density, e.g., 1-6 pounds per cubic foot of ethylenic polymer resin ( 16 to 96 kg / m 3) of foam is believed to enable commercial production. That is, it was believed that only dichlorotetrafluoroethane diffused out of the foam bubble sufficiently to suppress bubble wall collapse while air was slowly diffused into the bubble.

More recently, permeability modifiers or stability modifiers have been developed for incorporation into polyolefins in studies aimed at the slow diffusion of volatile hydrocarbon blowing agents from polyolefin foam bubbles. The purpose of these permeable modifiers is to make the foam more dimensionally stable against a wider range of volatile hydrocarbon blowing agents. For the purposes of the present invention the terms “permeable modifier” and “stability modifier” are generally used and refer to compositions which are incorporated into polyolefins to allow the volatile hydrocarbon blowing agent to slowly diffuse from the foam bubble walls. For example, US Pat. Nos. 4, 214, 054 to Watanabe et al. Describe a process for producing polyolefin foams using volatile hydrocarbon blowing agents. Permeability modifiers such as saturated higher fatty acid amides, saturated higher aliphatic amines and esters of saturated higher fatty acids are incorporated into the polyolefin composition prior to expansion.

Park's US Pat. No. 4,331,779 also describes an ethylenic polymer foam with improved dimensional stability, and describes a method of using copolymers of ethylene and unsaturated carboxylic acids as stability regulators. Park's US Pat. Nos. 4, 347, 329 describe the use of fatty acid amides, such as stearamido, for stability control in polyolefin foams. Park's US Pat. No. 4, 395, 510 also describes the use of fatty acid amide stability modifiers to produce polyolefin foams with improved elevated temperature dimensional stability.

The use of such permeable modifiers allows the use of a wider range of volatile hydrocarbon blowing agents. However, in most cases cheaper volatile hydrocarbon blowing agents such as butane can only be used in small amounts with other more expensive chloro- or fluorocarbons. When butane is used only as a blowing agent in a modified polyolefin foam, the foam exhibits a maximum percentage shrinkage of 10 to 20% as follows: (of the foam volume of the blade with the minimum volume relative to the volume of the foam immediately after expansion). B) x 100 = 10 to 20% (Reference Examples: Examples 21, 24 and 27 of Table 7 of US Pat. Nos. 4, 214, 054 to Watanabe et al.).

Accordingly, there is still a need in the art for low cost volatile hydrocarbon blowing agents that can be used to expand olefin polymers and can exhibit a high degree of dimensional stability with minimal shrinkage during quenching or curing of the polymer foam.

The present invention satisfies this need by providing an inexpensive modified olefin polymer composition having a high degree of dimensional stability and minimal shrinkage using inexpensive isobutane as the primary blowing agent and a method for producing the same.

According to one aspect of the invention,

(a) thermoplasticizing an olefin polymer resin selected from the group consisting of homopolymers of ethylene and copolymers of ethylene and copolymerizable monomers;

(b) a stability modifier selected from the group consisting of (1) partial esters of long chain fatty acids with polyols, higher alkylamines, fatty acid amides, olefinically unsaturated carboxylic acid copolymers, and polystyrene, and (2) ( Iv) isobutane, (ii) permeation rate of air passing through 5% to 95% of isobutane on the molar basis and the olefin polymer resin having a boiling point of -50 ° C to 50 ° C and modified by stability regulator A mixture with 95% to 5% of a physical blowing agent, selected from the group consisting of chlorofluorocarbons and fluorocarbons containing less than about 1.2 times and containing from 1 to 4 carbon atoms, and (iii) at least 70% of isobutane, Has a boiling point of -50 ° C to 50 ° C, a permeation rate through the olefin polymer resin modified by the stability regulator is greater than about 1.2 times the permeation rate of air, and 1 to 5 carbon atoms Containing, hydrocarbon, carbon tetrachloride, and mixed with a blowing agent selected from the group consisting of a mixture with physical blowing agent selected from the group consisting of chlorofluorocarbons and;

(c) activating the blowing agent to expand the mixture into an almost independent foam of olefin polymer foam, thereby providing a process for producing an almost independent foam of olefin polymer foam with dimensional stability. It was determined that there was a significant difference between the permeation rates of n-butane and its isomeric butanes through the polyolefin film modified by the stability modifier. n-butane has a permeation rate of greater than 1.0 while isobutane is only a ratio of 1.0 permeation rate of air. As such, it has been found that inexpensive isobutane blowing agents can be used alone or in combination with other volatile hydrocarbon blowing agents to produce dimensionally stable foams with low shrinkage during curing. The present invention has the further advantage that it is possible to use chlorine and fluorinated carbon which has been used so far or in a smaller amount. The impact of these volatile halogenated hydrocarbons on the ozone layer of the atmosphere is still a problem and it is desirable to minimize their use.

Various advantages of the invention will be apparent from the following detailed description and claims.

Suitable olefin polymer resins for the practice of the present invention include ethylene homopolymers such as low, medium or high density polyethylene and ethylene-vinylacetate copolymers, ethylene-propylene copolymers, ethyl-1-butene copolymers, ethylene-butadiene copolymers. Ethylene copolymers such as ethylene-vinyl chloride copolymer, ethylene-methyl methacrylate copolymer, ethylene-acrylonitrile copolymer, ethylene-acrylic acid copolymer and the like. Preference is given to using ethylene homopolymers or copolymers containing at least 50% by weight, preferably at least 75% by weight, of ethylene as the olefin polymer resin. It may also be appropriate to use mixtures of two or more of these olefin polymer resins in the practice of the present invention. Preferred compositions contain low density polyethylene and copolymers of ethylene and vinyl acetate.

Suitable stability modifiers for the present invention include partial esters of long chain fatty acids with polyols, as described in US Pat. Nos. 3, 644, 230, and US Pat. Nos. 4, 214, 054, described in US Pat. Such as higher alkylamines, fatty acid amides and higher fatty acids. Typically, these stability modifiers are used in amounts ranging from about 0.1 to about 10% based on the weight of the olefin polymer used.

In addition to or instead of the aforementioned stability modifiers, for this purpose, copolymers of various monoethylenically unsaturated carboxylic acids with α-olefins, such as those described in Park's US Patent Nos. 4, 347, 329, or in the art Copolymers of α-olefins with neutralized carboxyl group-containing moieties, commonly referred to as ionomers, can also be used. Typically, these olefinically unsaturated carboxylic acid copolymers can be used in amounts ranging from about 5 to 95 weight percent of the olefin polymer used.

Finally, polystyrene can be used as stability regulator in the present invention. Specific polystyrenes that can be used are described in Japanese Patent Laid-Open No. 55-181384. Typically these polystyrenes can be used in amounts ranging from about 5% to about 50% by weight of the olefin polymer used.

As already explained, the main feature of the present invention is the use of low cost isobutane as primary blowing agent in modified olefin polymer copolymers. Isobutane can be used alone as the only blowing agent. In addition, the isobutane blowing agent may include a mixture of one or more conventional physical blowing agents. Conventional blowing agents can be divided into two subgroups, groups I and II.

Therefore, the blowing agent contains 5 to 95% of isobutane on a molar basis and air passing through the modified olefin polymer with a normal boiling point of -50 to 50 ° C. and a permeation rate through the modified (by stability regulator) olefin polymer. A mixture with 95 to 5% of a physical blowing agent, selected from Group I consisting of chlorofluorocarbons and fluorocarbons, containing less than about 1.2 times the permeation rate and containing 1 to 4 carbon atoms, may be included. This permeation rate is measured by means of a test gas under the equilibrium vapor pressure of the gas at 23 ° C. at 1 atm or at 23 ° C. when the boiling point is at least 23 ° C. using the ASTM D-1434 method. Examples of physical blowing agents of these group I include dichlorodifluoromethane (FC-12), 1,2-dichlorotetrafluoroethane (FC-114), and 1-chloro-1, 1-difluoroethane (FC -142b). FC-12, FC-114 and FC-142b are trademarks of the products sold by DuPont.

If a blowing agent of group II is selected, the blowing agent passes through the modified olefin polymer with at least 70% isobutane and a normal boiling point of -50 to 50 ° C. and a permeation rate through the modified (by stability regulator) olefin polymer. A mixture with a physical blowing agent from group II selected from the group consisting of hydrocarbons, carbon chlorides, fluorocarbons, containing greater than about 1.2 times the permeation rate of air and containing from 1 to 5 carbon atoms. This permeation rate is also measured by the test gas under the equilibrium atmospheric pressure of the gas at 23 ° C. under a pressure of 1 atm or by a method of ASTM D-1434 or when the boiling point of the gas exceeds 23 ° C. Examples of physical blowing agents of group II include n-butane, isopentane, ethyl chloride, methylene chloride, trichloromonofluoromethane (FC-11) and 1, 1, 2-trichloro trifluoroethane (FC-113) There is this. FC-11 and FC-113 are trademarks of DuPont.

In the practice of the present invention, the blowing agent is formulated in a proportion capable of expanding the foamed foamed product produced in the starting material ethylenic polymer resin mixture to the desired degree, and is typically about 9.6 kg / m 2 (about 0.6 per cubic foot). Formulated to a volume expansion of about 60 times to produce a product having a dull foam density of up to pounds). Depending on the initial proportion of blowing agent, the resulting foam product of the invention has a relatively low foam density, for example, a density of about 9.6 to about 240 kg / m 2 [0.6 to about 15 pounds per cubic foot]. . Useful ratios of these blowing agents in the compositions of flowable foam gels are on the order of about 0.013 to about 0.50 gram moles per 100 g of starting material resin. The maximum useful proportion of blowing agent in the foamable gel is also influenced by the pressure held by the gel through the extrusion die, and when the die pressure is relatively high under conditions such as relatively small dioripes and / or relatively high throughput rates. Even bigger.

The blowing agent is blended in the starting resin mixture in a conventional manner, preferably in a continuous manner, for example by using heat in a mixing extruder to plasticize and pressurize the resin mixture to keep the expanding agent in a non-gas state and mechanical action. By completely mixing the resin mixture and the blowing agent to prepare a flowable gel. The resulting gel is then cooled if necessary and passed through a suitable die orifice to a region of low pressure, for example, normal ambient air temperature, where the gel expands into a low density foamy mass. When foamed and extruded, the gel is removed from the extruder and cooled to cure the resin mixture and recovered for further processing, storage and post use.

In addition to the components previously described, known nucleation (or bubble-sizing) agents (eg, talc, clay, mica, silica, titanium oxide, zinc oxide, calcium silicate, and barium stearate, zinc stearate) are known in the practice of the present invention. Other components or additives commonly used in known extrusion foaming methods such as latex, metal salts of fatty acids such as aluminum stearate and the like, wetting agents and the like.

In the following examples all parts and percentages are by weight unless otherwise indicated, and it is to be understood that these examples are intended to illustrate the invention and are not intended to be limiting in this range.

Example 1

The relative permeation rates of various physical blowing agents through the polyethylene film and polyethylene film modified with 2 pph of kemamide® S-180 stearyl stearamide stability modifier are measured. kemamide S-180 is commercially available from the Humko Chemical Division of Witco Chemical Corp. The results are shown in Table 1. Permeability data is measured using a modified ASTM D-1434 test method. As shown in Table 1, in the modified polyethylene, the permeation rate of isobutane relative to air is 0.31, and 1.58 for n-butane. In order to produce dimensionally stable polyolefin foams, the transmittance of the polymer to the blowing agent must be equal to or less than the transmittance to air. Otherwise, the foaming agent diffuses quickly from the foam bubbles during curing or quenching, causing shrinkage and loss of dimensional stability.

Example 2

The apparatus used in this example is a 1 1/2 inch (3.8 cm) screw type extruder comprising two additional sections for mixing and cooling at the end of a typical continuous section for injection, melting and metering. The blowing agent inlet appears between the metering section and the mixing section. Attach a die orifice with a rectangular hole to the end of the cooling section. The height of the hole is adjustable and its butterfly is fixed at 0.25 inches (0.635 cm).

TABLE 1

footnote

1. The polyethylene used in this test has a melt index of 2.3 and a density of 0.92 g / dl.

2. The film is left in the oven at 180 ° F. for 1 hour.

3. Penetration rate: 1 day in air ㏄ mil / 100 in ²

4. Permeability to air

Granular polyethylene having a melt index of 2.3 and a density of 0.923 g / cm 3 is mixed with a small amount (0.7 to 1.5 pph) of talc powder using a small amount of wetting agent. Except for the control formulation (Table II, Test No. 1), 25% Kemamide® S-180 stearyl, a product of the Humko Chemical Division of Witco Chemical Corp., was used to bring the concentration to 1.5 pph in the final polymer composition. Mix in sufficient amount in the polymer. The mixture is injected into the extruder at a substantially uniform rate of about 10 pounds per hour (4.5 kg per hour). The screw speed is maintained at about 45 rpm during the test. A blowing agent selected from the group consisting of isobutane and a mixture of dichlorodifluoromethane (FC-12) and isobutane is injected into the extruder at a predetermined rate. The temperature of the extruder section is fixed at about 115 ° C. in the inlet, 130 ° and 150 ° C. in the melting and metering section and 165 ° C. in the mixing section. The temperature of the cooling section is adjusted to drop the temperature of the polymer and blowing agent mixture to a uniform foaming temperature of about 108 ° C. The gap of the die hole is adjusted to ensure excellent foaming without preliminary foaming. Inlet die gaps range from 0.185 to 0.220 inches (0.47 to 0.56 cm). The nearly rectangular foam with rounded corners is separated from the die hole. Thickness and butterfly are 0.65 to 0.83 inches (1.65 to 2.11 cm) and 1.1 to 1.2 inches (2.8 to 3.0 cm), respectively. Foam samples of about 4 to 5 inches (10 to 12.7 cm) in length are cut from the strand and subjected to dimensional stability tests at ambient and elevated temperatures.

All blowing agents used in this example produce foams of good quality with low density and nearly independent bubble structure. The bubble size ranges from 0.8 to 0.9 mm. As indicated in Table II, the dimensional stability of all foams containing stearyl stearamide is excellent at ambient temperature and satisfactory at 165 ° F. The dimensional stability (Test No. I) of foams containing no permeable modifiers is not satisfactory. The results show that the dimensionally stable foams can be prepared from stearyl stearamide-modified polyethylene using isobutane or a mixture of isobutane and dichlorodifluoromethane (FC-12) as blowing agent.

TABLE 2

Footnotes:

(1) FC-12: dichlorodifluoromethane

(2) weight ratio of two blowing agents

(3) parts of mixed blowing agent per 100 parts of polymer

(4) part of kemamide S-180 stearyl stearamide (product of Humko Chemical Division of Witco Chemical Corp) mixed with 100 parts of polymer

(5) Density of the foam measured within about 5 minutes after extrusion (kg / ㎥)

(6) Time (in days) to reach minimum volume indicated as percentage of original volume

(7) the minimum volume of foam during standing at ambient temperature, expressed as a percentage of the initial volume measured within about 5 minutes after extrusion

(8) The volume of the foam, expressed as a percentage of the original volume, after being left at ambient temperature for a specified period of time.

(9) the minimum volume of the foam during standing at 165 ° F., expressed as a percentage of the initial volume.

Example 3

The apparatus used in this example is a 1 inch (2.54 cm) screw extruder having a shape almost the same as that used in Example 2. His operating procedure is almost the same. The butterfly of the gap-controlled die orifice attached to this foam extruder is 0.15 inch (0.38 cm).

The same polyethylene as used in Example 2 is mixed with 0.7 pph of talc and kemamide S-180 concentrate. The concentration of kemamide S-180 stearyl stearamide was kept the same at 1.5 pph in all tests of this example. The solid mixture is injected into the extruder using a weight injection device at a uniform rate of 5 pounds per hour (2.27 kg / hr). Isobutane or a mixture of isobutane and dichlorodifluoromethane (FC-12) is used as blowing agent. The temperature in the extruder section is fixed at 130 ° C. in the inlet, about 160 ° and 190 ° C. in the melting and metering section and 180 ° C. in the mixing section. The temperature of the cooling section is adjusted to cool the gel below a uniform temperature of about 111 ° C. Foam samples are taken from the die holes close to the preform inlet. The inlet die gap ranges from 0.065 to 0.080 inches (0.16 to 0.20 cm). The thickness and butterfly range of the foam cross section are 0.46 to 0.57 inches (1.17 to 1.44 cm) and 0.58 to 0.65 inches (1.47 to 1.65 cm), respectively. Foam samples of about 4 inches (10 cm) in length are cut from the strands and subjected to a dimensional stability test.

The test of this example is repeated for isobutane and a mixture (FC-12) of a wide mixing ratio of isobutane and dichlorodifluoromethane. Excellent quality bubbles with low density, low continuous bubble content and fine uniform bubble size are produced. Bubble size ranges from 0.8 to 1.6 mm. As indicated in Table III, all blowing agents provide foams that exhibit good stability at ambient temperature and satisfactory stability at 105 ° F. (similar to summer environmental conditions).

Example 4

In the test of this example, the same apparatus, the same solid composition and the operating procedure as in Example 2 were used. A mixture of 1, 2-dichloro tetrafluoroethane (FC-114) and isobutane is used as blowing agent. As shown in Table IV, the blowing agents produce high quality foams with excellent dimensional stability at ambient and high temperatures.

TABLE 3

Footnotes: All formulations contain 1.5 pph kemamide S-180 stearyl stearamide.

(1) FC-12: dichlorodifluoromethane

(2) weight ratio of two blowing agents

(3) parts of mixed blowing agent per 100 parts of polymer

(5) Density of blowing agent measured within about 5 minutes after extrusion (kg / ㎥)

(6) The time taken to reach the minimum volume, expressed as a percentage of the original volume, in days

(7) Minimum volume of foam during infiltration at ambient temperature, expressed as percentage of initial volume measured within about 5 minutes after extrusion

(8) The volume of the foam, expressed as a percentage of the original volume, after being left at ambient temperature for a specified period of time.

(9) the minimum volume of foam expressed as a percentage of the original volume during standing at 105 ° F.

TABLE 4

Footnotes: All formulations contain 1.5 pph kemamide S-180 stearyl stearamide.

(1) FC-114: 1, 2-dichlorotetrafluoroethane

(2) weight ratio of two blowing agents

(3) parts of mixed blowing agent per 100 parts of polymer

(5) Density of the foam measured within about 5 minutes after extrusion (kg / ㎥)

(6) Time (in days) to reach minimum volume expressed as percentage of original volume

(7) Minimum volume of foam during standing at ambient temperature expressed as percentage of initial volume measured within about 5 minutes after extrusion

(8) The volume of the foam, expressed as a percentage of the original volume, after being left at ambient temperature for a specified period of time.

(9) The minimum volume of the foam, expressed as a percentage of the original volume after incubation at 105 ° F.

As will be described in detail the invention and by the preferred forms of the invention, it will be apparent that modifications and variations are possible without departing from the scope of the appended claims.

Claims (5)

(a) Ethylene homopolymer, and ethylene-vinylacetate copolymer, ethylene-propylene copolymer, ethylene-1-butene copolymer, ethylene-butadiene copolymer, ethylene-vinylchloride copolymer, ethylene-methyl methacrylate copolymer Thermoplasticizing the olefin polymer resin selected from the group consisting of ethylene copolymers selected from the group consisting of ethylene-acrylonitrile copolymers and ethylene-acrylic acid copolymers; (b) the thermoplasticized resin is selected from the group consisting of (1) partial esters of polyols and long-chain fatty acids, higher alkyl amines, fatty acid amides, olefinically unsaturated carboxylic acid copolymers, and polystyrene, and (2) (i) iso Butane, (ii) the permeation rate through 5% to 95% isobutane on a molar basis and the olefin polymer resin having a boiling point of -50 ° C to 50 ° C and modified by the stability regulator is about 1.2 of the permeation rate of air. A mixture with 95% to 5% of a physical blowing agent, selected from the group consisting of chlorofluorocarbons and fluorocarbons, containing less than one fold and containing 1 to 4 carbon atoms, and (iii) at least 70% of isobutane and boiling point- 50 ° C to 50 ° C, wherein the permeation rate through the olefin polymer resin modified by the stability modifier is greater than about 1.2 times the permeation rate of air and from 1 to 5 carbon sources Containing the hydrocarbon, is mixed with a blowing agent selected from the group consisting of a mixture with physical blowing agent selected from the group consisting of carbon tetrachloride, and chlorofluorocarbons and; (c) activating the blowing agent to expand the mixture into an almost independent foam of olefin polymer foam, thereby producing an almost independent foam of olefin polymer foam having dimensional stability. The method of claim 1 wherein said ethylene copolymer is a copolymer with vinyl acetate. The method of claim 1 wherein the olefin polymer resin is low density polyethylene. The method of claim 1 wherein said stability modifier is a fatty acid amide. Product according to the method of claim 1.