WO2017096560A1

WO2017096560A1 - Method for manufacturing polyolefin foam

Info

Publication number: WO2017096560A1
Application number: PCT/CN2015/096824
Authority: WO
Inventors: 季国平
Original assignee: 季国平
Priority date: 2015-12-09
Filing date: 2015-12-09
Publication date: 2017-06-15

Abstract

The present invention discloses a method for manufacturing a polyolefin foam, wherein in the first step, a foamable polyolefin resin composition comprising a stabilizing agent, a cross-linking agent and a chemical foaming agent is heated under increased pressure for a period of time such that the foaming agent is partially decomposed, thus obtaining, upon pressure release, a preliminary intermediate foamed product; in the second step, heating the preliminary intermediate foamed product under atmospheric pressure until a degree of foaming is obtained such that part of the foaming agent remains undecomposed; and in the third step, further heating the foamed product obtained in the second step in a metal mold under increased pressure to decompose the remaining foaming agent, and then directly opening the mold without cooling the foamed product, thus obtaining a good foamed material.

Description

Method for producing polyolefin foam

Technical field

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a method for producing a polyolefin foam material, and more particularly to a method for producing a polyolefin foam material having a uniform, closed, microbubble thickness, which exhibits a low cost and high cost. Uniform physical properties of energy efficiency.

Background technique

Due to the excellent physical properties of this polyolefin foam, it has a wide range of uses. For example, bumpers, thermal insulators, acoustic insulators, protective sheets, packaging fillers, mat fillers, and various types of packaging.

Up to now, pressure foaming has been widely adopted as a polyolefin foam. Usually, this pressure foaming method is roughly divided into a one-step pressure method and a two-step pressure method. Incidentally, with the so-called one-step method, it is not easy to achieve a high expansion ratio by foaming itself, and it is not easy to obtain a product having a smooth surface. Efforts to make the foamed product have a smooth surface result in unfavorable results in reducing the thickness of the product, and the yield of the foam product calculated from the raw material is also lowered. Therefore, a two-step process is generally used to produce a polyolefin foam having a high expansion ratio.

A two-step method is described in the specification of Japanese Patent Publication No. SHO45 (1970)-29, 381 and the specification of U.S. Patent No. 3,098,832. In this method, a polyolefin mixture containing a crosslinking agent and a foaming agent is filled in a generally tightly sealed metal mold, and a crosslinking reaction occurs in the mixture at a decomposition temperature of the pressurization and the crosslinking agent. At the same time, keep the foaming agent from decomposing or dissolving the decomposed gas And remaining in the resin; the resulting compound is cooled and solidified while the resulting foamable flaky product is heated again under atmospheric pressure to cause foaming and expansion. Compared with the one-step pressure method mentioned above, this two-step method enables the foam to expand in three dimensions without causing surface damage, and thus is capable of producing a foam product having a good micro-foam at a high expansion ratio. If the flake-like foamable body is not heated and foamed in a metal mold under atmospheric pressure, a product having uneven thickness, rough surface, and unevenness is always obtained. If the skin of the surface of the rough foam product is scraped off to obtain a smooth hexahedral foam block, the consequent unfavorable result is that the yield of the product is low and the production cost is high with respect to the raw materials used.

The inventors have invented a method for preparing a foam material and applied for a patent. The method includes heating the metal sheet of the metal mold externally using the second step heating at atmospheric pressure as mentioned above, and a metal mold having a cross-sectional shape and size corresponding to the sectional shape and size of the final foam product. The intermediate intermediate foam product in the mold is heated indirectly to rapidly decompose the remaining foaming agent to obtain a polyolefin foam material having low density, uniform thickness and uniform physical properties (Japanese Patent Application Laid-Open No. SHO57 (1982)- 191,029).

When the above metal mold is used, after the completion of the second step, the mold and the built-in foam have been heated to about 150 ° C, which makes it difficult to remove the metal mold from the mold. In order to overcome this difficulty and to ensure a smooth surface foam, it is necessary to cool the metal mold after the second step and then remove the foam. Therefore, such an operation makes the energy utilization low, and the metal mold is alternately subjected to heating and cooling treatment, which is accompanied by low production efficiency. In addition, the piping through which the heating medium flows in the metal mold is also easily broken and needs to be repaired.

Summary of the invention

It is an object of the present invention to overcome the aforementioned difficulties and to provide a lower cost processing method for producing a thick foam having a uniform closed uniform micropores and having a uniform thickness and uniform physical properties; The method has high energy efficiency and high yield.

A method of producing a polyolefin foam of the present invention, the method is:

In the first step, the foamable polyolefin-type resin composition containing a stabilizer, a crosslinking agent and a chemical foaming agent is heated under pressure for a certain period of time to achieve partial decomposition of the above-mentioned foaming agent. Lowering pressure, thereby preparing a primary intermediate foam product;

In the second step, the primary intermediate foam product is heated under atmospheric pressure to be foamed to a certain extent such that a portion of the blowing agent remains undecomposed;

In the third step, in a metal mold and under pressure, the foam product obtained in the second step is further heated to decompose the remaining foaming agent, and then directly opened to obtain a good foam material without cooling the foam product. .

Further, the first step comprises charging the foamable polyolefin type resin composition into a tightly sealable metal mold, and heating the components in the mold to 130-280 under pressure. °C, maintained for 15 to 50 minutes, when the composition is heated to a pressure of 45-95% undecomposed in the blowing agent contained therein, the primary intermediate foam product is removed from the metal mold. The second step includes placing the primary intermediate foam product in a metal mold heated to a higher temperature without being tightly sealed, and indirectly heating the primary foam product to 130-280 ° C under atmospheric pressure to maintain For 15 to 50 minutes, it is further foamed until the degree to which 1-60% of the foaming agent is not decomposed remains.

Further, the third step includes making the bubble prepared in the second step In the case where the foam is pressurized in the original mold, heating is continued at 130-280 ° C until the remaining undecomposed foaming agent is completely decomposed, and then the mold is directly opened without cooling.

Specifically, the metal molds used in the second and third steps are the same, and are a metal mold that cannot be tightly closed.

More specifically, the metal mold that cannot be tightly closed is a braided metal mold having a tapered side wall that is larger than the lower surface.

Preferably, the braided metal mold housing is provided with a passage into which a heating medium can be introduced.

More preferably, the foamable polyolefin type resin composition is prepared by adding 1-5 parts by weight of a stabilizer to the polyolefin, based on 100 parts by weight of the polyolefin used, 5 to 35 parts of chemical blowing agent, 0.05 to 5 parts by weight of crosslinking agent, and appropriate amount of foaming aid, pigment, and sometimes filler to be added, and then, these compositions are in the 80-120 Mix well at a temperature of °C.

Further, the temperature of the kneading is 85-100 °C.

In this case, from the viewpoints of thermal efficiency and operational efficiency, it is desirable to use a metal mold which cannot be tightly closed at the time of heating under atmospheric pressure, and it is possible to continue using this under pressure during the next heating. Improved form of the mold.

The method of the present invention, after heating the first step of decomposing a portion of the blowing agent under normally applied pressure, further includes the following two steps as an unprecedented component of the method:

The primary intermediate foam obtained in the first step is subjected to a heating operation under atmospheric pressure to cause the primary foam to be foamed until a part of the foaming agent, preferably 1-60% of the foaming agent, is still in the Decompose the state (step 2); and

(B) The foam obtained in the second step is further heated under pressure to decompose the remaining foaming agent; the foam is directly opened without cooling, and a foam product is obtained (third step).

The operation of the above several steps and the relationship between them will be described below. First, the method of the present invention is different from the usual method in that after the crosslinking and foaming treatment is completed, the foamed product is directly opened without cooling (as described in (B)). As a general treatment, after the crosslinking and foaming treatment, the foam needs to retain sufficient residual expansion force so that it can be automatically expanded and can be detached from the mold after the metal mold is opened. This requirement is addressed in the above (A) component. To be more precise, when heating under atmospheric pressure, it is necessary to retain 1-60% of the blowing agent in the resin in an undecomposed state. When this is required, these undecomposed blowing agents are decomposed during the subsequent heating under pressure, resulting in the aforementioned residual expansion force. In order to achieve this, at least 1% of the blowing agent remains in the undecomposed state during heating under atmospheric pressure. If the proportion of blowing agent in the undecomposed state exceeds 60%, the expansion of the foam after opening the mold is too large, so that the foam will be easily broken or broken.

After heating under pressure as described in the above (B), a polyolefin foam having uniform physical properties and uniform thickness is obtained. As has been described, for the usual processing techniques, when foamed under atmospheric pressure, the physical properties and thickness of the resulting product lack uniformity due to unevenness in heat conduction. When the foam containing a part of the undecomposed foaming agent is heated in close contact with the inner surface of the metal mold, the foaming agent decomposes and foams, resulting in a pressurized state, so that the intermediate foam is under pressure The state of the metal mold plate is heated in the state of the entire circumference. Therefore, the heat transfer is satisfactory and the temperature distribution is uniform, so that a foam having uniform physical properties (e.g., density, compression hardness) and uniform thickness can be obtained.

When the foam is heated in a compressed state as described above and released after the metal mold is cooled, the cooling action of the mold causes the foam to cool and solidify without changing its shape. When the mold is opened in accordance with the method of the present invention before the metal mold has cooled, the resulting foam will expand to a shape and size similar to the shape and size of the mold cavity. Thus, a polyolefin foam having a high expansion ratio and a low density is obtained.

From the point of view that the foam is easily released from the mold, it is desirable that the side wall of the metal mold should be tapered so that the open end of the metal mold is wider than the bottom end thereof. The structure of the mold allows the foam to expand after opening the mold and automatically floats along the upwardly widened side walls.

The contents of the present invention are briefly described. First, a polyolefin type resin and a foaming agent, a crosslinking agent, and an additional co-blowing agent, a pigment, and the like are mixed together. Depending on the type of resin to be used, it is preferred to knead these components in a mixing machine such as a kneader, a kneader or a kneader at a high temperature in the range of 80 to 120 °C. Although the amount of the blowing agent and the crosslinking agent is reasonably determined depending on the expansion ratio to be achieved by the foam product; however, 1-5 parts by weight of the stabilizer are added in terms of 100 parts by weight of the resin used, 5 To 35 parts of the chemical blowing agent, the crosslinking agent is used in an amount of about 0.05 to 5 parts by weight.

Next, the crosslinkable and foamable composition obtained above is placed in a metal mold, tightly packed under pressure, and then heated to 120-180 ° C (preferably 140-170 ° C), maintaining 10-50. Minutes (preferably 15-35 minutes), thereby decomposing part of the blowing agent and part of the crosslinking agent. Thus, the pressure is released when the component is maintained at a relatively high temperature, and preferably 40 to 90% of the blowing agent is still not decomposed. The resulting primary intermediate foam is then removed from the metal mold. Usually, once the type of resin used, the crosslinking agent and the blowing agent, and the type and amount of the co-blowing agent are determined, The amount of residual undecomposed foam is determined by the heating temperature and heating time. Therefore, in actual operation, these relevant data are measured in advance, and thus, the heating temperature and the heating time can be selected so as to retain a predetermined amount of the undecomposed foaming agent. This method can be used to heat at atmospheric pressure, as will be described in detail later.

Furthermore, the primary intermediate foam produced as described above is incorporated into a metal mold which cannot be tightly closed, and preferably has a downwardly narrowed side wall, for example, a side wall having a tapered beak-like metal Mold. This has a larger area at the upper opening of the mold than at the bottom. The upper and lower sides of the mold are provided with two heated plates through which a heat medium such as steam or heating oil can pass, or two heated plates with heaters. By heating the hot plate medium on the mold, the primary foam is heated to 140-200 ° C (preferably 150-180 ° C) at atmospheric pressure for 10-50 minutes (preferably 15-30 minutes) until the resin There is also a 1-60% foaming agent left in an undecomposed state. In other words, the heating is carried out until 1 to 60% of the foaming agent remains undecomposed, and the primary foam fills the metal cavity due to expansion.

Finally, the foam obtained from the foregoing is usually left in the aforementioned metal mold and further heated to a predetermined temperature in the compressed state, that is, 140-200 ° C (preferably 150-180 ° C) until the remaining foaming agent is completely exhausted. Decomposed until. The foam then expands when it is opened without pre-cooling and automatically dislodges from the mold.

As is apparent from the above description, the method provided by the present invention has the following effects and advantages:

In addition to the natural cooling of the final product, the cooling step is not involved in the entire process, so the energy efficiency is high.

(b) Since the passage is provided in the second metal mold described above, only the heating medium is used, so that it is not severely worn, and also because of the heating medium and the cooling medium. There is no need to convert equipment, so equipment costs are low. In addition to the high energy efficiency mentioned above, the overall production cost is reduced.

(c) High operational efficiency. This is because the foam product has a residual expansion force after heating in a compressed state, and the side wall of the second metal mold is tapered, which is sufficient for the foam product to automatically escape from the mold.

(d) In the final heating step, the heat transfer to the foam is satisfactory, and the temperature distribution along the thickness direction of the foam is also uniform because the foam is used when the second metal mold is used. It is heated in close contact with the metal heating plate and in a compressed state. Therefore, it is easy to produce a thick foam material having uniform physical properties and having a uniform good closed micro-foam. In addition, since the foaming agent on the surface of the foam is completely decomposed, the surface of the foam material becomes smooth (the surface of the foam exhibits the color of the pigment when a pigment is added to the component for preparing the foam). Thus, the skin of the foam that has been cut off can be utilized as part of the foam.

The term "polyolefin" as used in the present invention includes various grades of polyethylene produced by high pressure process, medium pressure process, low pressure process, poly-1,2-butadiene, ethylene-propylene copolymer, ethylene-butyl Ethylene copolymer, ethylene-vinyl acetate copolymer, ethylene and a copolymer of acrylic acid or methyl methacrylate, ethyl ester, propyl ester and butyl ester in an amount of up to 45% by weight; their chlorinated derivatives (chlorine-containing) Up to 60% by weight), a mixture of two or more of the above polymers, and a mixture of the above polymers with isotactic or syndiotactic polypropylene.

The term "crosslinking agent" as used in the present invention refers to an organic peroxide which is a radical generating agent which is added to the above-mentioned polyolefin and which is required to have a decomposition temperature at least higher than that of the polyolefin. The temperature at which the melt begins to flow is higher. Under heating conditions, the organic peroxide generates free radicals that create bonds within or between the molecular chains of the polyolefin. Examples of organic peroxides include the following (but are not limited to these Medium): dicumyl peroxide, 1.1-di(tert-butylperoxide)-3,3,5-trimethylcyclohexane, 2,5-dimethyl-2,5-di (uncle Butyl peroxy)hexane, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexyne, α,α-bis(tert-butylperoxy)diisopropylbenzene, uncle Butyl ketone peroxide and tert-butyl peroxybenzoate. For a polyolefin used, it is necessary to choose the particular organic peroxide that is most suitable for it.

The blowing agent which can be used in the present invention is a type of chemical blowing agent which has a decomposition temperature higher than the melting point of the above polyolefin. Examples of blowing agents which can satisfy this requirement include, but are not limited to, the following: azo compounds such as azodicarbonamide and azo arsenate; nitroso compounds such as dinitros a pentamethylenetetramine and a trinitrosotrimethylenetriamine; a hydrazide compound such as P, P'-oxidized-bis(benzenesulfonylhydrazide); and a sulfonyl semicarbazide such as P, P '-Oxidation-bis(benzenesulfonyl semicarbazide) and toluenesulfonyl semicarbazide and the like.

In the process of the invention, it is also permissible to additionally add a foaming aid depending on the type of blowing agent used. Examples of the foaming aid are, but are not limited to, the range: a mixture containing urea as a main component; a metal oxide such as zinc oxide, lead oxide; containing salicylic acid, stearic acid, etc. as a main component a mixture of higher levels of fatty acids or higher levels of fatty acid metal compounds.

In order to achieve the objective of improving the physical properties of the composition used and reducing the cost of the product, the present invention allows for the additional addition of additives (fillers) which do not have any detrimental effect on the crosslinking reaction of the composition. Examples of additives are, but are not limited to, metal oxides such as zinc oxide, titanium dioxide, calcium oxide, magnesium oxide, silicon oxide, etc.; carbonates such as magnesium carbonate, calcium carbonate, fibrous materials, Such as pulp, dyes, pigments, fluorescent substances and additives usually added to rubber.

detailed description

The invention will now be specifically described by way of examples. In essence, however, the examples cited below are not intended to limit the invention in any way.

Example 1

formula:

The above components were uniformly dispersed and mixed. The mixture was placed in a first metal mold (bottom side area of 225 x 155 mm ² and height 16 mm), and the side wall of the mold was gradually widened with a compression molding machine thereon. At an external pressure of not less than 10 kg/cm ² , the mold was tightly closed and heated to 155 ° C for 17 minutes. When the foam is still maintained at a higher temperature, the pressure applied to the mold is removed while the primary foam is removed from the metal mold. The primary foam expands to a bottom edge area of 430 x 295 mm ² and a thickness of 35 mm (expansion ratio of approximately 8). About 75% of the blowing agent is not decomposed.

The primary foam after the mold release is immediately placed in a second metal mold in a braided shape at a higher temperature, and the side wall of the mold is gradually widened from bottom to top (the area of the upper opening is 680 × 520 mm ² , The bottom edge area is 600 x 440 mm ² and the height is 45 mm). Two hot plates were placed on the upper and bottom sides of the metal mold, and each plate had a passage for steam to be heated at 175 ° C for 15 minutes. As a result, the foam expands to fill the internal space of the aforementioned second metal mold (after this step, about 34% of the remaining foaming agent has not been decomposed). The foam thus obtained was further heated at the above temperature for 5 minutes. The mold is then opened to give a white foam having a uniform, well-closed microbubble.

Immediately after the foam material was taken out of the metal mold, the size of the foam was measured, wherein the size of the upper opening portion corresponding to the second metal mold was 780 × 600 mm ² , corresponding to the size of the foam at the bottom of the mold. It is 690 × 500 mm ² and the thickness is 52 mm. In fact, no residual blowing agent was found in the foam. The product obtained after natural cooling had an apparent density of 0.03 g/cm ³ and an expansion ratio of 30.

The expansion ratio and the residual amount of the above foaming agent are calculated by the following method (the calculations in the following examples are also the same):

Expansion ratio: expressed as the ratio of the size of the foam to the size of the first mold (thickness x bottom area).

Residual amount of blowing agent: expressed as 0 residual amount of blowing agent in the final product.

For example, the expansion ratio of the foam immediately after removal from the second mold is (690 × 500 × 52) / (225 × 155 × 16) = 32, and the residual amount of the foaming agent is 0%. For the obtained intermediate intermediate foam, the expansion ratio was (430 × 295 × 35) / (225 × 155 × 16) = 8; the residual foaming amount was (32 - 8) / 32 × 100 = 75%. For the foam which has been foamed under atmospheric pressure in the second step, the expansion ratio is (600 × 440 × 45) / (225 × 155 × 16) = 21, and the residual foaming dose is (32-21). /32×100=34%.

Example 2

formula:

The components in the above formulation were uniformly dispersed and mixed. The resulting mixture was then heated under pressure according to the procedure in Example 1 to prepare a primary foam. The reaction conditions were changed as follows: The first mold had a bottom side area of 245 x 180 mm ² and a height of 32 mm, and was heated at 155 ° C for 35 minutes. The primary foam expands to a size of 440 x 320 mm ² corresponding to the bottom edge of the mold and has a height of 70 mm (expansion ratio of about 7). Approximately 82% of the foaming agent in the foam remains undecomposed.

The primary foam was then heated at atmospheric pressure in accordance with the procedure of Example 1 (at the end of this step, approximately 55% of the blowing agent remained undecomposed), followed by continued heating under compression. Different from the first embodiment, the above-mentioned primary foam is placed in two second metal molds, and then the two mold mouths are joined together to heat and foam, and the two braided second The size of the metal mold was the same as that of the second mold used in Example 1.

As a result of measuring the foam just taken out of the mold, the size of the intermediate portion (corresponding to the opening portion of the second metal mold) was 885 × 680 mm ² in the upper side and the lower side portion (corresponding to The bottom of the second mold has a size of 800 x 580 mm ² and a thickness of 115 mm. The foam is actually provided with a residual undecomposed blowing agent. The resulting product is a white, having a uniform, good foam body closed microbubbles, an apparent density of 0.03 g / cm ^3, expansion ratio of about 30.

Example 3

The primary foam was prepared as in the procedure of Example 1.

The primary foam was placed in the same second metal mold as used in Example 1, and heated at 175 ° C for 15 minutes by the same heating method. After the end of the heating, it will already The second step of foaming which expands and fills the inner space of the mold is taken out of the mold. At this time, the undecomposed residual foaming amount was about 34%.

The foam of the second step is placed in a third metal mold having the same dimensions as the second metal mold described above. It was then tightly closed and heated at 175 ° C for 5 minutes as in the second metal mold heating method. Subsequently, the mold was opened to obtain a microbubble foam material having a uniform, well-closed shape. This foam material had the same dimensions as the final product of Example 1 when it was taken out of the mold.

Claims

A method for producing a polyolefin foam, characterized in that the method is:

In the first step, the foamable polyolefin-type resin composition containing a stabilizer, a crosslinking agent and a chemical foaming agent is heated under pressure for a certain period of time to achieve partial decomposition of the above-mentioned foaming agent. Lowering pressure, thereby preparing a primary intermediate foam product;

In the second step, the primary intermediate foam product is heated under atmospheric pressure to be foamed to a certain extent such that a portion of the blowing agent remains undecomposed;

In the third step, in a metal mold and under pressure, the foam product obtained in the second step is further heated to decompose the remaining foaming agent, and then directly opened to obtain a good foam material without cooling the foam product. .
The method of producing a polyolefin foam according to claim 1, wherein said first step comprises charging said foamable polyolefin type resin composition into a metal mold which can be tightly sealed, under pressure The component in the mold is heated to 130-280 ° C for 15 to 50 minutes, and when the composition is heated until the blowing agent contained therein is still 45-95% undecomposed. Pressing, removing the primary intermediate foam product from the metal mold; wherein the second step comprises placing the primary intermediate foam product in a metal mold that is heated to a higher temperature and is not tightly sealed, under atmospheric pressure, The primary foam product is indirectly heated to 130-280 ° C for 15 to 50 minutes for further foaming until the extent to which 1-60% of the blowing agent is not decomposed remains.
The method for producing a polyolefin foam according to claim 1 or 2, wherein the third step comprises, in the case where the foam obtained in the second step is pressurized in the original mold, Heating was continued at 130-280 ° C until the remaining undecomposed blowing agent was completely decomposed, and then the mold was directly opened without cooling.
The method for producing a polyolefin foam according to claim 1 or 2, wherein the metal mold used in the second step and the third step is the same, and is a metal mold which cannot be tightly closed.
The method of producing a polyolefin foam according to claim 1 or 2, wherein the metal mold which is not tightly closed is a braided metal mold having a tapered side wall which is larger than the lower surface.
The method of producing a polyolefin foam according to claim 1 or 2, wherein the braided metal mold outer casing is provided with a passage into which a heating medium can be introduced.
The method for producing a polyolefin foam according to claim 1 or 2, wherein the foamable polyolefin type resin composition is prepared by using 100% by weight of the polyolefin used in the polyolefin. Calculated by adding 1-5 parts by weight of stabilizer, 5 to 35 parts of chemical blowing agent, 0.05 to 5 parts by weight of crosslinking agent, and appropriate amount of foaming aid, pigment, and It is sometimes necessary to add fillers, and then these compositions are kneaded uniformly at a temperature of 80 to 120 °C.
The method for producing a polyolefin foam according to claim 7, wherein the kneading temperature is 85 to 100 °C.