Foam having less variation in diameters of air bubbles, and method for producing the same

Abstract

To provide a foam which has small air bubbles included in a surface layer of a foam, is easily deformed by a defoaming step because of less variation in diameters of air bubbles and thereby is excellent in work efficiency, and facilitates formation of a communication hole by the defoaming step and thereby is excellent in restorability.SOLUTION: A foam is obtained by foaming a resin composition, wherein when a layer located less than 2 mm from the surface of the foam is defined by a first layer, and a layer located 2 mm or more and less than 5 mm from the surface thereof is defined by a second layer, an average value of diameters of air bubbles included in the first layer and the second layer is 0.25 mm or more and 0.50 mm or less, and an absolute value of a difference between a maximum value of diameters of air bubbles included in the first layer and a maximum value of diameters of air bubbles included in the second layer is 0.05 mm or more and 0.15 mm or less.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a foam formed by foaming a resin composition. Specifically, the foam has small bubbles enclosed in the surface layer, and since the variation in the size of the bubbles is small, it can be easily defoamed by a defoaming process, so it is a foam with excellent working efficiency. Moreover, since it is easy to form through-holes by the defoaming process, it relates to a foam with excellent resilience.

Background Art

[0002] Generally, a method for manufacturing a foam by in-mold molding is to knead a resin composition and a foaming agent, etc. while heating, press the kneaded mixture into a mold for filling, crosslink the resin composition, and then release the press to foam the resin composition for manufacturing.

[0003] The manufactured foam can be compressed with a roll or the like to break the bubble film to form ventilation holes, or to connect independent holes to form through-holes.

[0004] When there are many through-holes, it becomes a foam with excellent resilience.

[0005] However, if the foam is difficult to defoam, there is a problem that it is necessary to repeatedly compress it with a roll or the like to form ventilation holes or through-holes, and the working efficiency is poor.

[0006] Therefore, the development of a foam that is easy to defoam, easy to form ventilation holes and through-holes, has excellent working efficiency, and also has excellent resilience of the foam is desired.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0008] Patent Document 1 describes a method for producing a crosslinked polyolefin continuous foam in which a foaming composition containing a polyolefin is foamed and then mechanically deformed to communicate the cell membranes.

[0009] However, the foam described in Patent Document 1 has a problem that it is difficult to defoam, so it is necessary to repeatedly perform the step of applying mechanical deformation, resulting in poor working efficiency.

[0010] The inventors of the present invention made it a technical problem to solve the above problems, and as a result of repeating many trial productions and experiments through trial and error, a foam obtained by foaming a resin composition, where when less than 2 mm from the foam surface is the first layer and 2 mm or more and less than 5 mm is the second layer, the average value of the diameters of the cells included in the first layer and the second layer is 0.25 mm or more and 0.50 mm or less, and the absolute value of the difference between the maximum value of the diameters of the cells included in the first layer and the maximum value of the diameters of the cells included in the second layer is 0.05 mm or more and 0.15 mm or less. Such a foam has excellent defoaming properties, is easy to form ventilation holes and communication holes, has excellent working efficiency, and also has excellent resilience of the foam. The inventors obtained a remarkable finding and solved the above technical problem.

Means for Solving the Problems

[0011] The above technical problem can be solved by the present invention as follows.

[0012] The present invention is a foam obtained by foaming a resin composition, where when less than 2 mm from the foam surface is the first layer and 2 mm or more and less than 5 mm is the second layer, the average value of the diameters of the cells included in the first layer and the second layer is 0.25 mm or more and 0.50 mm or less, and the absolute value of the difference between the maximum value of the diameters of the cells included in the first layer and the maximum value of the diameters of the cells included in the second layer is 0.05 mm or more and 0.15 mm or less.

[0013] The present invention is also the above foam, where the resin composition is a polyolefin resin.

[0014] The foam of the present invention is also the above-mentioned foam in which the polyolefin resin is a polyethylene-vinyl acetate copolymer.

[0015] The foam of the present invention is also the above-mentioned foam in which the polyethylene is low-density polyethylene.

[0016] The present invention also provides a method for producing a foam, in which a foamable resin composition is first heated by a press in a closed system and then secondarily heated in an open mold. The secondary heating is carried out by heating twice at different temperatures.

Advantages of the Invention

[0017] The foam in the present invention has small bubbles in the surface layer and little variation in size, so it has excellent defoaming properties. By compressing with a metal roll or the like, the bubble film is quickly broken, and defoaming occurs to form ventilation holes and communication holes, so it is a foam with excellent working efficiency.

[0018] Also, since it is easy to form communication holes, it is a foam with excellent resilience.

[0019] Also, if the resin composition is a polyolefin resin, the foam will have excellent weather resistance, chemical resistance, and water resistance.

[0020] In particular, if the polyethylene is low-density polyethylene, the resin composition can be kneaded at a low temperature.

[0021] Also, after the foamable resin is first heated and then heated twice at different temperatures, the bubbles on the surface layer of the foam can be made small and the variation in size can be reduced, and a foam with excellent defoaming properties can be produced.

Embodiments for Carrying Out the Invention

[0022] The foam in the present invention is a foam in which the average value of the diameters of the bubbles (hereinafter referred to as "average bubble diameter") contained in the surface layer less than 5 mm from the foam surface is small.

[0023] The average bubble diameter included in the surface layer is preferably 0.25 mm to 0.50 mm, more preferably 0.28 mm to 0.35 mm.

[0024] This is because if the average bubble diameter is less than 0.25 mm or greater than 0.50 mm, the defoaming property deteriorates.

[0025] In addition, the foam in the present invention is a foam with little variation in the diameter of the bubbles in the surface layer.

[0026] Specifically, the absolute value of the difference between the maximum value of the bubble diameter in the layer less than 2 mm from the surface (hereinafter referred to as the "first layer") and the maximum value of the bubble diameter in the layer of 2 mm or more and less than 5 mm (hereinafter referred to as the "second layer") is 0.05 mm to 0.15 mm.

[0027] The foam in the present invention has an average bubble diameter included in the surface layer of 0.25 mm to 0.50 mm and little variation in the diameter of the bubbles in the surface layer, so it is a foam excellent in defoaming property.

[0028] The foam in the present invention is produced by foaming a resin composition.

[0029] The resin composition is not particularly limited, but a polyolefin resin is preferable. This is because it is excellent in weather resistance, chemical resistance, and water resistance.

[0030] Examples of the polyolefin resin include polyethylene, ethylene-vinyl acetate copolymer, polypropylene, polytetrafluoroethylene, ethylene-propylene copolymer, poly-4-methyl-1-pentene, polyvinyl chloride, polyvinylidene chloride, polyvinylidene fluoride, tetrafluoroethylene, and ethylene copolymer.

[0031] The polyethylene may be low-density polyethylene. If it is a low-density polyethylene-vinyl acetate copolymer, the melting point of the resin composition decreases, so it can be kneaded at a low temperature.

[0032] The resin composition in the present invention contains a foaming agent.

[0033] The foaming agent is not particularly limited, and examples thereof include organic chemical foaming agents such as azodicarbonamide which is an azo compound of azodicarbonamide, barium azodicarboxylate, dinitrosopentamethylenetetramine and trinitrotriethylenetriamine which are nitroso compounds, p,p'-oxybisbenzenesulfonylhydrazide which is a hydrazide compound, p,p'-oxybisbenzenesulfonyl semicarbazide and toluenesulfonyl semicarbazide which are sulfonyl semicarbazide compounds. Also, an inorganic foaming agent such as sodium bicarbonate can be used.

[0034] The foaming agent is preferably 3 to 20 parts by weight, more preferably 6 to 18 parts by weight, based on 100 parts by weight of the resin composition.

[0035] If it is less than 3 parts by weight, there is a risk that sufficient foaming may not occur, and if it exceeds 20 parts by weight, there is a risk that a foam cannot be formed.

[0036] A foaming aid may be added to the resin composition of the present invention to adjust the foaming rate.

[0037] A crosslinking agent may be added to the resin composition in the present invention.

[0038] The crosslinking agent is not particularly limited, and examples thereof include dicumyl peroxide, 1,1-di-tert-butyl peroxide, 1,1-di-tert-butylperoxy-3,3,5-trimethylcyclohexane, 2,5-dimethyl-2,5-di-tert-butylperoxyhexane, 2,5-dimethyl-2,5-di-tert-butylperoxyhexyne, α,α-di-tert-butylperoxyisopropylbenzene, tert-butyl peroxy ketone, and tert-butyl peroxy benzoate.

[0039] The crosslinking agent is preferably contained in an amount of 0.2 to 3 parts by weight, more preferably 0.5 to 1 part by weight, based on 100 parts by weight of the resin composition.

[0040] This is because if the crosslinking agent is less than 0.2 parts by weight, there is a risk that rigidity cannot be obtained, and if it is contained in an amount exceeding 3 parts by weight, there is a risk that a foam will not be formed.

[0041] A crosslinking aid may be added to the resin composition of the present invention in order to adjust the crosslinking rate.

[0042] A filler may be added to the resin composition of the present invention.

[0043] The filler is not particularly limited, and examples thereof include calcium carbonate, calcium oxide, diatomaceous earth, titanium oxide, graphite, and starch.

[0044] An antioxidant, a pigment, etc. may be appropriately added to the resin composition of the present invention.

[0045] The manufacturing method of the present invention will be illustrated.

[0046] The resin composition, the foaming agent, and, if necessary, the crosslinking agent, the foaming aid, the filler, etc. are added, kneaded by a heated mixing roll, a pressure kneader, an extruder, etc., and the obtained kneaded product is filled into a mold.

[0047] The mold filled with the kneaded product is sealed under a pressure of 20 kgf / cm 2 ~150 kgf / cm 2 and subjected to primary heating at 120°C to 140°C for 30 to 60 minutes to produce an intermediate product.

[0048] The intermediate product obtained by the primary heating is placed at approximately the center of an airtight openable / closable metal mold provided with a hot steam flow path around it, heated at 130°C to 150°C for 20 to 40 minutes under atmospheric pressure, then heated at 160°C to 170°C for 60 to 180 minutes. After confirming filling into the mold due to foaming, it is cooled to obtain a foam.

[0049] By increasing the temperature in two stages and performing secondary heating, the surface bubbles can remain small, and the cross-linking that was insufficient during the primary heating can be promoted.

[0050] Through primary and secondary heating, the blowing agent and cross-linking agent are decomposed. After confirming the filling in the mold during secondary heating, the foam is produced by cooling.

[0051] The produced foam can be manufactured into a foam with pores and through-holes formed by sandwiching it from above and below with metal rolls and compressing it to break the cell membranes.

Example

[0052] The present invention will be described in more detail with reference to examples and comparative examples, but the present invention is not limited thereto.

[0053] The resins and additives used in the examples and comparative examples are shown in Table 1.

[0054]

Table 1

[0055] As shown in Table 2, for 100 parts by weight of the resin, each additive was added in each part by weight to produce each resin composition with foamability. Then, primary heating, secondary heating were performed, and cooling was carried out to obtain the foams of the examples and comparative examples.

[0056] Each foam was evaluated as follows.

[0057] (Tension) The appearance of the foam was observed, and those without dents or wrinkles due to shrinkage etc. were evaluated as "〇", and those with dents or wrinkles were evaluated as "×".

[0058] (Foam) The appearance of the foam was observed, and those without cracks or entrapment in the foam were evaluated as "〇", and those with cracks or entrapment were evaluated as "×".

[0059] (Defoaming property) A foam with a thickness of 100 mm was compressed with a metal roll rotating at a speed of 12 rpm to break the bubble film of the foam and defoam it.

[0060] The foam was pressed with a finger, and when it was confirmed that it no longer had the same firmness as before defoaming, the defoaming was considered complete.

[0061] The foams that could be defoamed with less than 10 compressions of the metal roll were evaluated as "◎", those that could be defoamed with 10 to 19 compressions were evaluated as "〇", and those that could not be defoamed without being compressed 20 times or more were evaluated as "×".

[0062] (Resilience) After heating each defoamed foam with a thickness of 100 mm at 70 °C for 1 hour, the thickness was measured.

[0063] The foams with a thickness of 95 mm or more after heating were evaluated as "◎", those with a thickness of 85 mm or more and less than 95 mm were evaluated as "〇", and those with a thickness of less than 85 mm were evaluated as "×".

[0064] (Bubble diameter) Each foam of the examples and comparative examples was cut with the layer less than 2 mm from the surface as the first layer, the layer from 2 mm to less than 5 mm as the second layer, the layer from 5 mm to less than 10 mm as the third layer, the layer from 10 mm to less than 20 mm as the fourth layer, and the layer from 20 mm to less than 40 mm as the fifth layer. The diameter of the bubbles (bubble diameter) appearing on the upper and lower surfaces of each layer was measured using the 3D shape measurement software VHX - H5M of the digital microscope VHX - 8000 (manufactured by Keyence Corporation).

[0065] The average value was calculated from the measured bubble diameters of each layer (average bubble diameter).

[0066] The absolute value of the difference between the maximum values of the bubble diameters of the first and second layers was calculated (difference in maximum bubble diameter).

[0067] The results are shown in Table 2 and Table 3. Note that in Table 3, "maximum bubble diameter" represents the maximum value of the bubble diameters of each layer, and "minimum bubble diameter" represents the minimum value of the bubble diameters of each layer.

[0068]

Table 2

[0069]

Table 3

[0070] From Table 2 and Table 3, it was proved that the foam in the present invention has a small average cell diameter on the surface layer, is uniform, has little variation, and is excellent in defoaming property and resilience.

Industrial Applicability

[0071] The foam in the present invention has small cells encapsulated in the surface layer and little variation in size, so it is easy to defoam. Therefore, it is a foam with excellent working efficiency because it can be easily defoamed by the defoaming process. Moreover, it is a foam with excellent resilience because it is easy to form through-holes by the defoaming process. Therefore, the present invention is an invention with high industrial applicability.

Claims

1. A foam obtained by foaming a resin composition, wherein when less than 2 mm from the foam surface is the first layer and 2 mm or more and less than 5 mm is the second layer, the average value of the diameters of the bubbles contained in the first layer and the second layer is 0.25 mm or more and 0.50 mm or less, and the absolute value of the difference between the maximum value of the diameters of the bubbles contained in the first layer and the maximum value of the diameters of the bubbles contained in the second layer is 0.05 mm or more and 0.15 mm or less.

2. The foam according to claim 1, wherein the resin composition is a polyolefin resin.

3. The foam according to claim 2, wherein the polyolefin resin is a polyethylene-vinyl acetate copolymer.

4. The foam according to claim 3, wherein the polyethylene is low density polyethylene.

5. A method for producing a foam, comprising primary heating a foamable resin composition with a press in a closed system and then secondary heating in an open mold, wherein the secondary heating is performed by heating twice at different temperatures, the method for producing a foam according to claim 1 or 2.