IE44520B1 - A continuous process for producing variable hardness polyurethane molded paris - Google Patents

Abstract

A CONTlNUOUS PROCESS FOR PRODUCING VARIABLE HARDNESS POLYURETHANE MOLDED PARTS The instant invention generally relates to the continuous production of variable hardness molded polyurethane foam parts. Hardness of a foam is a function of the density of the foam and the index of the foamable reaction mixture. These variable hardness parts are continuously produced by the controlled addition of an inert blowing agent which directly affects density. These parts may also be produced by utilizing the double effect of controlling both the addition of the blowing agent and the foam index.

Description

Methods for producing molded polyurethane foam of various hardnesses are well known. For given types of reaction compoents, it is possible to vary the degree of hardness by varying the foam index, the foam density, the extent of major chemial modification and any combinations thereof. The foam index is a measure of the isocyanate/ hydroxyl ratio and generally the higher the index, the harder the resultant foam. Foam density is primarily dependent on the amount of reaction mixture added to the mold (overpacking is a frequent technique), the amount of water added to the mixture just prior to addition to the mold (the more water, the more COg is produced as a blowing agent), and the amount of inert blowing agent used. The extent of major chemical modification refers to the type and amount of crosslinking agent(s) used in the foamable mixture. Generally, the more crosslinking, the more rigid and hard the foam. Thus, with the manipulation of any of these parameters and in addition thereto selecting the proper isocyanate, polyol and other additives, a foam part can be made with virtually any desired hardness and flexibility.

As the demand for polyurethane foam parts has risen, so has the demand that the foam be used in a variety of appliations. An example of this demand is in the furniture industry where such items as chairs and couches would advantageously have soft backs and firmer seats for better comfort. In the industry today, the furniture is made by attaching separate pieces together or by utilizing one piece of intermedite hardness. The disadvantages in cost and/or compromise in quality are readily apparent.

It has been found that it is possible to continuously produce single molded polyurethane parts of variable hardness by introducing into a mold a foamable reaction mixture comprising: (a) an organic polyisocyanate (b) a first blowing agent (c) a polyhydroxyl compound having a molecular weight from 200 to 10,000, wherein (1) the amount of component (b) which is used is varied or (2) in addition to varying the amount of the first blowing agent, the amount of component (a) and/or (c) is also varied.

In one particularly preferred embodiment, a second blowing agent is also included in the foamable mixture.

Introduction means may be provided which allow said foamable reaction mixture to be directed to various parts of the mold at any given time.

The amount and rate at which the first, and optional second, blowing agent is added as a component in foamable reaction mixture directly affects the density and hardness of the foam. The higher the amount, the less dense and the softer the foam; the lower the amount the denser and harder the foam. Similarly, by. varying the amount of either the polyhydroxyl compound or the polyisocyanate or both, the foam index is altered. Generally, the higher the foam index the harder the foam.

Generally, the various components are fed to a mixing head before introduction into the mold. The rates at which each stream enter the mixing head can be controlled by any of various known techniques. The single stream exiting the mixing head flows to a closed mold through a mold aperture or may flow to an open mold by known open pour techniques. It is generally necessary to include some means of directing the foamable reaction mixture to the various parts of the mold so that the proper formulat44520 - 4 ion at any given time will go to that part of the mold which is to have the particular hardness corresponding to the given formulation. The use of a closed mold with a slot or slots may be particularly advantageous.

Depending on the mold configuration and the degree to which the hardness of the ultimate part is to vary, it may be advantageous to have means for rotating the mold itself in a number of directions.

Any materials suitable for making molded polyurethane foams may be used.

Suitable polyisocyanates include but are not limited to aliphatic, cycloaliphatic, araliphatic, aromatic and heterocyclic polyisocyanates. Those generally used are the commercially readily available polyisocyanates such as 2,4- and 2,6-tolylene diisocyanate and mixtures of these isomers (TDI); polypheny! polymethylene polyisocyanates of the type obtained by condensing aniline with formaldehyde, followed by phosgenation (crude MDI); and modified polyisocyanate such as those containing carbodiimide groups, urethane groups, allophanate groups, isocyanurate groups, urea groups or biuret groups.

Suitable polyhydroxyl compounds include those having molecular weights of from 200 to 10,000. Such compounds are well known and include certain polyesters, polyethers, polythioethers, polyacetals, polycarbonates, polyester amides, polyamides. These compounds should contain at least 2 and preferably 2 to 4 hydroxyl groups reactive with isocyanates.

Various catalysts, chain extenders, emulsifiers, foam stabilizers, reaction retarders, cell regulators, pigments or dyes, flame retarding agents, stabilizers against the effects of ageing and weathering, plasticizers, substances with fungistatic and bacteriostatic effects and fillers may be used in the process and are generally added to the polyol stream prior to its addition to the mixing head. 4 5 2 0 Water and/or readily volatile organic substances are used as the blowing agents. Suitable inert blowing agents include acetone; ethyl acetate; methanol; ethanol; halogen-substituted alkanes, such as methylene chloride; chloroform; ethylidene chloride, vinylidene chloride; monofluoro- trichloromethane; chlorodifluoromethane; dichlorodifluoromethane; and butane, hexane; heptane; and diethyl ether. A blowing effect may also be obtained by adding compounds which decompose spontaneously at temperatures above room temperature, giving off gases such as nitrogen. Examples of such compounds include azo compounds such as azoisobutyronitrile. Further examples of blowing agents and details on the use of blowing agents may be found in Kunststoff-Handbuch, Vol. VII, published by Vieweg and Hochtlen, Carl-Hanser-Verlag, Munich (1966), pages 108 and 109, 453-455 and 507-510.

In order to produce a cellular polyurethane part, it is necessary to use in the foamable reaction mixture a blowing agent or a compound such as water which creates a blowing agent (C02) as it reacts with isocyanate groups.

For purposes of this invention, the term blowing agent is intended to include water as well as the other types of organic and inorganic blowing agents known in the art.

Thus, if it is desired to completely stop the introduction of the first blowing agent into the foamable mixture, the foamable mixturemust contain a second blowing agent to insure that the final molded part is cellular. It would, of course, also be possible to use water as the sole blowing agent.

The various possible reactive formulations of the above-mentioned compounds and the foams of various densities produced thereby, the various methods for preparing these formulations, and various methods for filling molds are well known, e.g. U.S. Patents 3,182,104; 3,188,296 Saunders and Frisch, Polyurethanes, Chemistry and Technology, Part 11, pages 1-299, which are herein incorporated by reference.

The instant invention is not directed towards any specific 45 20 formulations, nor any particular closed or open mold processing methods, nor foams with any particular density range.

The following are examples of parts which have been made by the process of the invention. There are intended for illustration and are not intended in any way to limit the scope and spirit of the invention. All components are parts by weight of resin blend unless otherwise specified.

EXAMPLES Articles were made using two different closed molds, one in the form of a chair, (Examples 1, 2 and 3) and the other in the form of a small love seat (Examples 4, 5 and 6). Articles weighing from 13 to 16 lbs. were made with average densities ranging from 1.6 to 2.5 Ibs/ft , The initial mold «1 11 temperature in each case was maintained at 95 ± 5 F to insure good skin quality of the foam. Those portions of the mold which were not to receive the foamable reaction mixture which contained the first blowing agent were kept at lower temperatures, preferably at 75° - 80°F. Demolding was achieved in each case in approximately 10 minutes.

In each case the foaraable reaction mixture was introduced into the mold through an aperture via a pipe from the mixhead. The pipe was connected to the mixing head in such a way that it could be rotated. Between the mixing head and the mold aperture, a pipe T was attached to the pipe to enable manual rotation of the pipe. Inside the mold a 90° reducer was attached to the end of the pipe to form a discharge tube. In this way, the reaction mixture could be laterally directed to the mold extremities.

In each example, the resin blend consisted of 100 parts of a polyether polyol (trio! initiated propylene oxide with a molecular weight of about 6000). 2.7 parts water 1.5 parts amine catalysts 1.0 parts silicone surfactants In each instance, the osocyanate was an allophanate polyisocyanate based on toluene di isocyanate, dissolved in 4 5 2 0 TDI, with an NCO content of 40.5%.

The blowing agent used was monofluorotrichloromethane. % blowing agent used below means pbw based on resin blend.

In the examples, the relative amounts of resin blend, isocyanate, and blowing agent in each formulation are given by denoting (1) the foam index and (2) the 1 blowing agent. The foam index is the equivalent weight ratio of isocyanate/ polyol X 100. The % blowing agent is a weight measure based on the amount of resin blend used. Note that the % blowing agent refers only to the amount of monofluorotrichloromethane and not to the blowing agent produced by chemical reaction, e.g. between water and isocyanate.

To delineate the schemes used in the examples, Table 1 shows a number of combinations of streams which enter the mixing head directly or in combination with one of the other streams and the general effects on the hardness as the blowing agent stream is reduced to zero and/or the index is changed.

As an example of the various streams entering the mixing head, in Technique A, stream la meets stream 1 near the mixhead. Subsequently, the combined stream 1/la enters the mixhead where it mixes with stream 2. 4520 UJ CQ < (Λ (/) Φ Ρ P ds on trennths (/) Ρ υ φ 1 (ρ «ρ 4— 4- <ι> Ο cn Φ £ Ε Φ Φ £ σι χ ·<- xj XZ JZ Φ Ρ Ρ ρ 2 cn 2 cn ό. φ Ρ (0 ο •r— O •r· Φ -ε «Ρ Φ X Γ— XZ ·“ XX L Ω Ρ ο (Λ P p X Φ Φ Ρ Φ φ Φ - _E xz φ -σ ε' ε - 2 σι cn 2 c (0 (0 O •i— •1— ο f—I (Λ W r™ xz JZ >i P P p Ρ (Λ Φ Φ φ 'Γ* XZ xz χζ C 2 cn 2 cn cn Φ Ο •p- o •t— o •γ— Q 4= i— JZ χζ XJ Π3 Φ X cn P £ - E Ρ •r~ Φ £ X O) Φ r— σι Σ cn < Φ c cn jz •r- Ε 4-» 2 •γ· O 35 Ο r— Ο Ρ 4-> m Γ— £ CQ (Λ XJ Φ X) X) XJ XJ XJ \ X» ε ε σι φ c Ε Ε Φ £ Φ £ Φ Φ £ Φ (0 φ «=ε ρ φ Φ Φ Φ P Φ P Φ P Ρ Φ Ρ Φ (0 r- -P r— r- ro r· (0 r- (0 (0 Γ— (0 ρ co cn c 03 <0 CQ CQ £ 03 £ CQ £ £ CQ £ Ρ £ «3 C «3 <0 (0 (0 (0 tn £·«- >> £ t0 c c >» C >> £=>>>> £ >» •r- 2 O ·«“ >> (j ·*- O •r- O υ ♦«- ς> (/) WOO w Q (Λ Ο) O V) O (/) o ο (Λ Ο 3 Φ r— V> Φ O Φ φ (Λ Φ (/) Φ (/) φ (Λ Ο GJCQH O' (Λ OZ ΟίΗ CZ >~t C£ W Η-1 QZ ·—· •Γ* Ρ Λ <0 nJ (0 > ·«— T- CM *—CM CM r- CM t- CM CM CM Φ •σ ο t—< t—t W S 1—< h-« 1—1 H-) )—i 1—1 φ 3 σ* Γ £ X ο φ I— < CQ Ο ί «4520 In technique A, mode I, two streams enter the mixing head, an isocyanate stream and a mixed stream of resin blend and blowing agent. In technique A, mode II, the blowing agent stream is turned off leaving only an isocyanate and resin blend stream to enter the mixing head. The effect of turning the blowing agent stream off is that the resultant formulation produces a denser and harder foam than in technique A, mode I. In technique B, both the amount of blowing agent and the foam index is changed between modes I and II by turning off a third resin blend/ blowing agent stream to the resin blend stream and thus to the mixing head. The result is a double effect upon the hardness. Technique C was not actually carried out but is included for illustrative purposes. If the index is lowered by removing an isocyanate stream the general effect would be to lower the hardness of the foam. On the other hand, by reducing the amount of blowing agent in the formulation, the tendency would be to raise the hardness of the foam. Thus, the overall effect would depend on the relative strengths of the offsetting effects.

In Examples 1, 3 and 4 (note Table 2), a reaction mixture for making softer, flexible foam (Mode I, Technique A) was injected into that part of the mold corresponding to the back of the chair or love seat. At a given time, the inert blowing agent stream was shut off and while reaction mixture was still flowing into the mold, the discharge tube was rotated towards the seat portion of the seat or chair (Mode I, Technique A).

In Example 2, a reaction mixture for making softer, more flexible foam (Mode I, Technique B) was introduced towards the back portion of the mold. At a given time, the stream carrying both the mixture of resin blend and inert blowing agent was shut off and while the reaction mixture was still flowing into the mold the discharge tube was rotated towards the seat part of the mold (Mode II, Technique B). 4 5 2 0 In each case various sample parts of the molded foam were tested for density and hardness. The results are presented in Table 2. Seat and back position No. 3 in Table 1 refer to samples taken from just either side of the dividing line between the hard and soft portions of the molded part. Positions No. 1 refer to samples taken from the extreme ends of the seat or chair and Positions No. 2 refer to intermediate locations. In each case, the density was measured in lbs/ft . C.L.D. is a hardness p measure in Ibs/in (ASTM-D-2406-73; Compression Load Deflection at 50% Compression). <3· CO| oj| ΙΛ CD Ο Ο \ \ co co Ι*χ Γ-- CO «3· Ο co *4· 'χ.

CD LO *tf- LD OJ 04 Lf} Ο *3- *5f «Τ OJ OJ 04 Ο «φ r- CV1 OJ LU CQ < OJ *4* «fr CO CO CO CQ OJ 00 ω io id χ-, \ cn co σ» O LQ o \ X. \ o < m co IX is r- OJ 0J 0J OJ 0J o >> p ‘f1/) c Φ Q P 4-) C C Φ Φ cn co < < r— 0J CO 1— OJ co X Φ X Φ cn cn =te =*fc =¾ 4fe * Ό •σ c c C c C C c c c c •r- •r- O o o o o o 1—4 4—4 £ S •r— •r— •r- «Γ— *r~ •r- O o P P P P P P ε ε r— J— «π- 'r- ‘1— ·Γ“ •f— •r~ c0 (0 CQ CQ ω ω ω ω ω ω Ο o O O O ο o O Lu U. S-5 cu Q_ cu Q_ CU cu X^, x^. P jX p .X -X A>£ .X P P P tO Q «0 υ Ό υ u to to (0 Φ <0 Φ rO nJ (0 «0 Φ Φ Φ CO CQ CO CO CQ CQ CQ co to to 4520 - 12 The results in Table 2 show that a single molded part can be continuously produced with separate zones of hardness. Note, for example. Example 1 where the hardness in the back portion averages 0.33 psi while the seat portion averages 0.64 psi. In Example 4, a dye was added, to the blowing agent. Remarkably, the dyed and colorless sections of the chair are not separated by any significant semi-colored transition area and yet each molded part was quite homogeneous and not weak at the demarcation line.

In Examples 5-6, seats were produced with either a hard core and a soft surface or vice-versa. As above, this was done continuously by manual control over the direction of the discharge tube and a blowing agent rate change on the fly. Table 3 shows the densities and hardnesses at various locations in each of three parts which were made. In each case, the foam index was held constant at 105. Surface position 1 was near the top of the back while surface position 2 was at the front of the seat portion. Core positions 1-4 were located at various places within the core, generally beginning at the back and working towards the seat. 54520 TABLE 3 EXAMPLES 6 Core/% Blowing Agent 0 15 Surface/% Blowing Agent 15 0 Surface Pos. 1) 1.72/.17 - Surface Pos. 2. 1.81/.32 2.57/.41 jDensity/C.L.D.

Core Pos. 1 j 2.34/.34 - Core Pos. 2 ) 2.23/- 1.92/.17 Core Pos. 3 , - 1.96/.21 / Core Pos. 4 ) 2.54/.38 1.96/.23 4452®

Claims (8)

1. CLAIMS:1. A process for the continuous preparation of single molded polyurethane parts of variable hardness comprising introducing into a mold a foamable reaction mixture comprising: (a) an organic polyisocyanate (b) a first blowing agent (c) a polyhydroxyl compound having a molecular weight from 200 to 10,000 wherein the amount of component (b) which is used is varied.

2. A process as claimed in Claim 1 wherein, in addition to varying the amount of said first blowing agent, the amount of component (a) and/or component (c) is also varied.

3. A process as' claimed in Claim 2 wherein, in addition to components (a), (b) and (c), a second blowing agent (d) is included in the reaction mixture.

4. A process as claimed in Claim 3 wherein, the amount of said second blowing agent is held constant throughout said continuous preparation.

5. A process as. claimed in Claim 4 wherein, at some time prior to completion of the process the introduction of said first blowing agent (b) is stopped.

6. A process as claimed in Claim 5 wherein said second blowing agent (d) is water and said first blowing agent (b) is monofluorotrichloromethane.

7. A process for the continuous preparation of single moulded polyurethane parts of variable hardness substantially as hereinbefore described with reference to the accompanying examples.

8. Single moulded polyurethane parts of variable hardness whenever prepared by a process claimed in a preceding claim.